Please send a hand history in which this issue occurs to hm2support@holdemmanager.com with a link to this thread.
All original hands that are auto-imported get moved to an archive for performance reasons. Your \HM2Archive is in C:\HM2Archive by default, but you may have put it anywhere. The archive should be organized by \Month\DayOfMonth (example: D:\HM2Archive\2009\07\31).