Can't delete A2K notices

Have you tried clearing cache and temporary files on your computer? Also, has the computer been rebooted after doing the above?

Can't delete A2K notices
I'll try your suggestions, but I'm curious: why only A2K notices?

Can't delete A2K notices
All of a sudden, the problem has disappeared.

Go figure.

You didn't specify what you are talking about (e.g. how you read your email) but it sounds like a desktop client like Outlook or Outlook Express.

And it sounds like the mail client crashed and when you restarted it (you may not have noticed the crash) the files were kept in use. Killing some hung processes can sometimes do the trick for this kind of problem but a sure solution is almost always just to reboot the computer if you aren't comfortable hunting down and killing processes and threads.