Error Message: "Item has not been assigned a class" - But it has!!

Entering hours on timesheet (QB Premier 06 - Acct & Bkpr), and entering Cust:Job, Service Item, Payroll Item, and Class. Window comes up: "One or more items have not been assigned a class. Save anyway or cancel and return to the form?"

Save Anyway does save the info, and it appears it reports everything OK. I tried 'Cancel' a couple times, and then tried to re-save - always got the error message.

Once I changed the class (to one that actually better matched to Cust:Job), it accepted it no problem.

I've looked to see if there's anything in the Class or Item list that seems relevant, but haven't found anything.

Anyone have any idea what would cause this behaviour??