I'm using Thunderbird for 64-bit Windows, release version 102.3.3.

Same thing started happening to me in just the last few days. Like Cindy, I've emptied my Trash folder, done compacting on it (as well as Inbox and Sent folders) -- multiple times. I've also gone into Windows Explorer and deleted Trash and Trash.msf files, then let Thunderbird rebuild. (Ditto for deleting and rebuilding the gargantuan Global Database.) Also used the right-click-on-folder-->Properties-->Repair Folder for Trash and Inbox.

But no matter what I've tried, the problem persists when I try to delete *multiple* messages from my Inbox. This doesn't really seem to be an issue with the Trash folder "not having enough room," since I *can* delete those exact same messages one-by-one, regardless of their size.

Also, I can even delete *two* messages at a time; however, when I select three (or more) messages to delete (no matter how small they are), I see the same error that Cindy is reporting.

Would be nice if someone from the support team would answer!

This is probably a third party anti virus program scanning in the mail folder while Thunderbird is trying to save stuff there. Generally there needs to be an exception in the antivirus to prevent it accessing the Thunderbird profile folder.

I'm using McAfee AV. It doesn't allow for adding an entire folder to its "Exclusion" list, but I did try adding the individual global database ("global-messages-db.sqlite"), as well as the "Trash" and "Trash.msf" files to the McAfee exclusion list.

However, that made no difference to the new, previously-reported Thunderbird behavior "can delete one or two messages at a time, but 3 or more" results in the error message.

I'm reluctant to turn off McAfee's real-time scanning entirely just to make this go away.

Well, Matt was right: I turned off McAfee's real-time scanning entirely, and the Thunderbird problem went away. (BTW, it wasn't just a "can't delete more than two messages at a time" problem -- it was also happening any time I tried to *move* more than two messages from one email folder to another.)

I could see no way to selectively disable email scanning in my version of McAfee (a freebie provided as part of a Cox account).

I resurrected Microsoft's "Security Essentials" real-time scanning, and it seems not to be as intrusive as McAfee's. At least, with the MSFT scan running in the background, I can still move or delete many Thunderbird messages in one "swell foop" without the annoying error message reported earlier.