Once in a while, my Notes client crashes. When it does, the count of unread mail in my inbox is wrong: it seems to write the new number into the desktop only on exit, and if the exit doesn’t go according to plan, the inbox unread counter is out. [This is just my observance: those with real info could let me know if this is right!]
Anyway, I found a quick workaround. Go to the trash folder and select everything. Select Edit->unreadMarks-> mark selected read. Voila!
Jim Cantor.