Try compact your folders:

• CompactFOlders

Also:

• Safe Mode

OK, I tried compacting folders and it didn't help. By the way, the docs say that if you use File > Compact Folders, you'll see a progress bar in the status bar, but I don't. Maybe it's really fast? I tried compacting some folders individually too.

The problem still happens in Safe Mode.

I don't know if it's relevant, but the Error Console shows a lot of messages like:

Warning: Found unclosed string '"publicly>'. Unexpected end of file while searching for closing } of invalid rule set. Source File: about:blank Line: 1007, Column: 4 Source Code: <id="publicly>

Yes, is very fast the compacting.

Hmmm, i think this will solve the problem, first unhide the hidden files and folders:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

Then go to your profile:

• How do i find my profile?

Enter in the ImapMail or Pop3Mail folder >>Enter in imap.xxxxx or pop3.xxxxx >> Enter in [Webemail].sbd >> Delete all .msf archives

Thanks for trying, but deleting all the .msf files did not fix it the problem.

What is your anti-virus s/w?

No anti-virus software.

Since deleting all the .msf files, I have a new symptom: Warnings like

"The messages could not be filtered to folder 'Xcode' because writing to folder failed. Verify that you have enough disk space, and that you have write privileges to the file system, then try again."

I do have around 10 GB of disk space, and can't find anything wrong with the ownership or permissions. I note that the folders giving me this error are ones where the .msf file has not been recreated.

I suspect I may be affected by this bug.

This error message can be solved if you repair the folder.

OK, thanks, repairing affected folders did get rid of the messages about inability to filter.

Try reinstall the Thunderbird:

• http://www.mozilla.org/en-US/thunderbird

Already tried removing and reinstalling Thunderbird.

Try these steps.

http://kb.mozillazine.org/Compacting_folders#Real_fix

christ1, the trouble is, it's not just the Inbox that's having a problem. For instance when I'm composing a reply, TB is unable to copy the message to Drafts. And if I select a message in some random folder and try to move it to some other random folder, TB does nothing.

Just to rule this out as a potential cause of the problem, can you try to start Thunderbird in safe mode?

http://support.mozillamessaging.com/en-US/kb/safe-mode

The suggestions given so far were more or less assuming a local problem with your profile, or some sort of corruption. May be this assumption was wrong.

What is your account type, POP or IMAP?

christ1, the first reply I got suggested Safe Mode, and as I said above, I tried it and the problem still happened.

I have 4 POP accounts and one IMAP.

With which of those 5 accounts do you see the problem?

I see the problem in all of the accounts.

I have no other ideas than trying with a new profile. Create a new profile using profile manager, and set-up one account at a time. Verify if you still see problems after setting up each account.

https://support.mozilla.org/en-US/kb/using-multiple-profiles

Also use profile manager to start Thunderbird with the new profile.

I can delete messagen in safe mode. Don't know if this can help, I got these warnings:

(process:14159): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' failed

(thunderbird:14159): GLib-GObject-WARNING **: Attempt to add property GnomeProgram::sm-connect after class was initialised

(thunderbird:14159): GLib-GObject-WARNING **: Attempt to add property GnomeProgram::show-crash-dialog after class was initialised

(thunderbird:14159): GLib-GObject-WARNING **: Attempt to add property GnomeProgram::display after class was initialised

(thunderbird:14159): GLib-GObject-WARNING **: Attempt to add property GnomeProgram::default-icon after class was initialised

Then I started Thunderbird in safe mode with these options: - Disable all add-ons; - Reset all toolbars and controls.

It's working fine, but extensions and themes are disabled. Enabled extensions one by one and no problem.