Try to rebuild the index file of the troubled folder.

Right-click the folder - Properties - Repair Folder

Hiya christ1,

Many thanks for replying. It is all the folders.(But I did try it on one folder just to check and to be honest it done nothing at all click repair and nothing) No folder is now displaying new messages even though I know there should be messages in there ( Yes, I use filters to put new messages into certain folders ) I did check and yes the filters are still there. Now I will say it is a Pop3 account and NOT an IMAP one.... Yes I know you will say should make it IMAP but for what i use it for that is not practical. It is better as a POP3 account. At the moment I have gone into account settings and stopped Thunderbird from checking, downloading or otherwise anything even on startup.... I am assuming that something in the update did not go as planned and it has corrupted the account folder. Another thing I note is that when it does go and try and download messages. down the bottom left it is saying downloading say 22 of 50 but that message is not showing anywhere at any point so it is not as if is going into a folder then disappearing.... But it is deleting it from the server (which is why have stopped it checking) Normally when it downloads messages you see it moving it to the appropriate folder as soon as got it..... Am not seeing anything that I would class as normal.

I know am probably giving too much information. But would sooner give you too much information than not enough. Could the entire user profile be corrupted? and is there a way to repair / rebuild that ??

Ok it is all fixed. Found the solution.

I deleted all the .MSF files and restarted and now it seems to be working fine except the filters are no longer working. But, I have just deleted them and reset them back up and they too are now working fine.