Thunderbird occasional email problems

Hi,

Sometimes Thunderbird 1.0 (on Win 2000 Pro) doesn't download my emails 
from the pop3 server. However if I go to my webmail and delete all the 
spam and junk, leaving only emails I wish to keep, and then try again 
Thunderbird has no problem and downloads them fine. Why is this and how do 
I fix it? This keeps happening at least once every 2 days.

Regards,

MS