I'm very sorry about that.
Since I deactivated automatic polling for the news account and set the time to 0minutes. I did not have the problem any longer. Could it be the 100min in the news account somehow confused yamb?
I read my code again and again but can't find any connection between the pop3 global inbox check, and the news (nntp) check. And I don't manage the rss check. (I don't know if you speak about a nntp or a rss account when you mention your news account).
My conclusion would be that you did not encounter this error after cancelling the news check just by chance, but I'm not very confident about this. Anyway, if there is a link, I don't see where and how.
Maybe you could try to change the 100 minutes setting ? For example, get the news account every 60 minutes, and see if sometimes you only get your pop3 accounts every hour ?
Would it be possible to start a completely new cycle after manually checking mails?
For this, I must hook on the GetMail button (and menu) to call a Yamb function. This may be possible, but is likely to break every other extension which does the same thing. I'll have a look, but this will probably not definitely solve your problem:
there still is the standard automatic mail check of Thunderbird, happening about 60 times less often, and which may cause the same trouble. (In fact, yamb does it's mail check, considering the mail biff interval in seconds, but Thunderbird keeps going with it's own checks considering the interval in minutes)