
Most likely the database file got corrupted. Be careful though if you have some messages in your "Storage Folders" as these are NOT on the server and they are only on your PC and deleting would lose them permanently.

That is why I asked, because with POP, the messages are downloaded and are stored on your PC. Since you use IMAP, the messages are stored on the server, that means you can safely delete the data folder and it will recreate it and download messages again.

Windows update did not kill it although it might be related.

The data store of Windows Live Mail got corrupted.
