I can't download new messages

Hello,

I installed the Thunderbird portable edition (version 2.0.0.16 (20080708)), for a while. It has been working perfectly until last update.
Now it keeps trying dowload all messages from the 15.th of january until 20.th of July then stops and tell me "there are no new messages on the server" (there are quite a lot !).

I try to delete profiles, to re install the programm (old and updated versions).... always the same !

Thank you for your help.