TB duplicate email downloads

I have both an EMachine T5212 and Toshiba laptop with Thunderbird 2.0.0.16 installed on each. This past month I have been getting multiples of some of my emails (not all emails only several) that keep getting downloaded. Some are Imap some are stmp accts. But why would I get from 4 - 75 of one email each time I log on? I can have 50 messages waiting for download and they will download correctly. However, the one I downloaded on 8/8/08 keeps download multiple times. How can I stop this? Both machines run XP sp3. There are only several (maybe 3 or 4 messages that keep repeating). I have checked with the people that sent them and the word is it is not on their end. Help please!!