How to fix iCalendar errors 0x804a0106, 0x804a0107 and 0x804a0108
One of these three codes just popped up in Thunderbird or another calendar app, and the number in yours decides the fix. Match it below, two of the three are not even your fault.
By Neeraj Singh ~12 min Updated Jul 2026 89% found this helpful
Seeing “0x804a0107”, the file error? Your events are not lost, the app was simply blocked from reading or writing its calendar file, or was handed data it could not treat as a calendar. Check your permissions on the file and folder, close anything else holding the file and make sure the disk is not full. Importing or pasting something? Check that data too. Method 2 walks you through it.
“0x804a0106”, the internal error? This one is not your fault, something broke inside the app's own calendar engine. Update the app, restart it and try again, that clears it for most people. Huge calendar? Method 5 shows the split trick.
“0x804a0108”, the usage error? Also not your fault, and not your file's either. The app used its own calendar engine in the wrong order, which is a bug. Update the app, and if the code survives, Method 6 shows what to report.
Not sure which code you have? Press Ctrl+Shift+J in Thunderbird (Mac: Cmd+Shift+J) to open the Error Console and read it off the red line, Method 1 decodes it with you.
Three codes, three very different culprits
The hex form of these codes is how Thunderbird and its older Lightning add-on report faults from their calendar engine, which is built on the libical library. Other apps built on the same library report the same faults by name, such as ICAL_FILE_ERROR, without the hex. They sit right next to the parse error 0x804a0105, but none of the three is about broken event syntax. Your only job before fixing anything is to read which number you have, because it names the culprit for you: the file around your calendar, the engine itself or the app that drives it.
Figure 1: which code you have decides who fixes it
✓ How to fix it
Find your code's methods below, they are grouped so you never read fixes for a code you do not have. Each one tells you what success looks like, so you know when to stop.
Method 1
Read the exact code in the Error Console
1In Thunderbird press Ctrl+Shift+J (Mac: Cmd+Shift+J) to open the Error Console, then repeat the action that fails, an import, a save or opening the calendar.
2Read the red line. It shows the code and, in square brackets, the function that raised it, for example [calIICSService.parseICS]. A parse function means the data being read is suspect, a write operation means the file is.
3Note whether yours ends in 06, 07 or 08, then jump to that code's methods. You will know this step worked when you can name your code and the operation it failed in.
Figure 2: how to read the Error Console line
Method 2
0x804a0107: fix access to the calendar file
1A local Thunderbird calendar is just an .ics file, usually inside your profile folder. Check that your user account can read and write both the file and the folder it sits in, permission problems here also surface as MODIFICATION_FAILED alerts when you save an event.
2Close any other program that might be holding the file open, sync tools and backup software are the usual suspects, then confirm the disk is not full and the file's path still exists.
3Retry the action. You will know it worked when the event saves or the calendar opens without the alert. Still failing with permissions fine? The data itself may be the problem, go straight to Method 3.
Method 3
0x804a0107: check the data you imported or pasted
1This code is not only about file access. Mozilla's calendar has raised 0x804a0107 from its parser when handed content that was not calendar data at all, for example plain text pasted into the calendar view.
2Open the .ics you were importing in a plain text editor. A healthy calendar starts with BEGIN:VCALENDAR and ends with END:VCALENDAR. Anything else, an HTML page, an email body, an empty file, will be rejected.
3If the file looks like a calendar but still refuses, its syntax may be broken rather than missing: run it through an online iCalendar validator, or follow the 0x804a0105 parse error guide to validate and repair it. A clean re-export from the original source fixes most cases.
Method 4
0x804a0106: update the app and restart
1An internal error means the calendar engine tripped over itself, which is a bug or a bad state, not something you caused. Update Thunderbird or your calendar app to the latest release, engine bugs get fixed in updates.
2Restart the app fully, and the computer if the error has been frequent, to clear any stuck state. Close other heavy programs before retrying so the app has room to work.
3You will know it worked when the same action runs clean after the restart. If the code returns on one specific calendar only, Method 5 finds the trigger.
Method 5
0x804a0106: split a large calendar to find the trigger
1If the internal error only fires on one big calendar, size or one specific event is provoking the bug. Test with a smaller .ics or a copy holding only a few months of events.
2The small file imports fine? Split the original into parts and import them one by one, the part that fails contains your trigger event.
3Delete or re-create that one event at the source and re-export. Success looks like the full calendar importing with the trigger removed.
Method 6
0x804a0108: update the app, then report the bug
1A usage error is the app calling its own calendar engine out of sequence. There is nothing to fix in your file or your events, so do not edit the .ics.
2Update the app first, the buggy call may already be fixed. If the code survives the update, report it to the developer with the exact steps that trigger it and the full Error Console line from Method 1, that line is exactly what a developer needs.
3Need the calendar working today? Open the same .ics in a different calendar app as a workaround, it will almost certainly load there.
Method 7
Rebuild the calendar: new calendar, re-import the .ics
1For stubborn repeats of any of the three codes on a local calendar, the calendar's own storage may be in a bad state. Locate its .ics file and copy it somewhere safe first.
2Create a brand new local calendar in the app, then import the saved .ics into it. This is the standard community fix for a misbehaving Thunderbird calendar and takes about two minutes.
3Your events appearing in the new calendar without the code is your confirmation. Delete the old calendar once you are happy everything arrived.
Do not edit the .ics for a 0106 or 0108, the file is almost certainly fine and you risk creating a real parse error on top. Editing is only ever on the table for a 0107 whose data check in Method 3 fails.
Where the 0x804a01 error family comes from
The calendar engine behind Thunderbird and many other tools defines a set of error types for the different ways an operation can fail, and the app reports them as hex codes in this 0x804a01 family. The neighbour you may already know is 0x804a0105, the parse error for broken event syntax. Your three sit directly after it, and the numbering is no accident: the last digits follow the engine's own ordered list of error types, which is why parse lands on 05 and these land on 06, 07 and 08. Codes that close together always come from the same machinery, which is the reason one page can cover all three.
This is why the fix changes completely with the last digit. Two of the codes describe software misbehaving, where your only sensible moves are updating and reporting. Only the file error describes something in your own environment, permissions, locks, disk space, a moved folder or bad input data, which is why it is the one code here you can fully fix yourself.
Common causes behind each code
Your account lacks permission on the calendar file or its folder (0x804a0107).
The file is locked by a sync or backup tool, the disk is full or the path moved (0x804a0107).
Imported or pasted content is not valid calendar data at all (0x804a0107).
A bug or unrecoverable state inside the calendar engine (0x804a0106).
One oversized calendar or a single problem event provoking the engine (0x804a0106).
The app calls the calendar engine out of order, a programming bug (0x804a0108).
An out-of-date app carrying an engine or usage bug already fixed upstream.
Expert insight
“The trick with these three is to read the code, not the panic. A 0107 is the only one that is yours: the system would not let the app at the file, or the file you fed it was never a calendar, and ten minutes sorts either. A 0106 or a 0108 is the software's problem, so I update first and report second. The one thing I stop people doing is opening the .ics in an editor for a 0108, the file is perfectly fine and they are about to hand themselves a genuine parse error as a bonus.”
Manager, Tech Support & Operations · 19+ years fixing Windows and system errors
Make sure this is the error you have
Two neighbours are easy to mix up with these. If your code is 0x804a0105 or the message names ICAL_PARSE_ERROR, the event syntax inside the .ics is broken and the parse error guide is your page. And if Thunderbird shows MODIFICATION_FAILED with a reason like NS_ERROR_FILE_ACCESS_DENIED when you save an event, that is the same file-access family as 0107, so Method 2 above applies. Apple Calendar on a Mac saying “There was an internal error attempting to save this import” is also not 0x804a0106, that is Apple's own import fault, not a Thunderbird engine code. And a calendar that fails to update over the network with an account or server alert is a different problem again, covered in the calendar couldn't be refreshed guide.
Frequently asked questions
What do errors 0x804a0106, 0x804a0107 and 0x804a0108 mean?
The hex codes are Thunderbird's way of reporting faults from its calendar engine, built on the libical library, and each points at a different layer. 0x804a0106 is an internal fault inside the engine. 0x804a0107 is a file or data problem, and 0x804a0108 means the app itself used the calendar engine incorrectly. The number decides the fix, so identify it first.
How do I fix 0x804a0107 ICAL_FILE_ERROR?
Fix access to the calendar file first: check your permissions on the file and its folder, close any app holding the file open, free disk space and confirm the path exists. If you were importing or pasting data when it appeared, also check the data itself, because feeding the parser something that is not a valid calendar can raise the same code.
What causes 0x804a0106 ICAL_INTERNAL_ERROR?
An unexpected breakdown inside the calendar engine, usually a bug in the app version you are running or a state the engine could not recover from. Update the app, restart it and retry. If it only appears on one large calendar, split the calendar and import it in parts to find the trigger.
What is 0x804a0108 ICAL_USAGE_ERROR?
It means the app called its calendar engine out of sequence, which is a programming mistake in the app, not a problem with your file or your events. Update the app, and if the error survives the update, report it to the developer with the steps that trigger it.
Where do I see the full error message in Thunderbird?
Open the Error Console with Ctrl+Shift+J on Windows and Linux or Cmd+Shift+J on a Mac, then repeat the action that fails. The red entry shows the code plus the function that raised it in square brackets, which tells you whether it happened while parsing, reading or writing.
Is my .ics file the problem?
For 0x804a0106 and 0x804a0108 almost never, the fault is in the software. For 0x804a0107 it can be either access to the file or the content you fed in: a healthy .ics starts with BEGIN:VCALENDAR, so open it in a text editor and check, or run it through the parse error guide for 0x804a0105.
Why do I get 0x804a0107 when my permissions are fine?
Because the same code can be raised while parsing, not just while reading or writing. Pasting or importing something that is not calendar data at all has been recorded producing 0x804a0107 in Mozilla's calendar. If permissions, locks, disk space and the path all check out, inspect the data you gave the app.
Is MODIFICATION_FAILED the same problem?
It is the same family. When Thunderbird cannot write to a local calendar it often shows an alert with MODIFICATION_FAILED and a reason such as NS_ERROR_FILE_ACCESS_DENIED underneath. The cure is the file access fix: permissions on the profile folder, disk space and nothing else locking the file.
Still not working?
If a 0107 persists after every access check, the calendar file may sit somewhere your account genuinely cannot use, a protected system folder or an offline cloud path, so move it to a local folder you own and point the app there. For a stubborn 0106 or 0108, open the same .ics in a different calendar app: it loading cleanly is your proof the fault is app-side, which makes Method 7's rebuild or a bug report the way forward. Browse the full set of iCalendar and ICS error guides for anything adjacent, or submit your error to us for a tailored fix.
