There is an old issue that we all hoped Macrodobia would have fixed in the release of Flash 8. The issue of classes conflicting due to the server timestamp being a few minutes ahead of your local timestamp will cause Flash to spit out a class conflict error. This little extension will alieviate all of your woes:

http://www.macromedia.com/cfusion/exchange/index.cfm?extid=1016963&view=sn111

Once installed, this extension will add two commands to the “Commands” menu in Flash called “Clear ASO and Compile” and “Clear ASO cache”.

Since installing this extension, I have not had an issue.