We have Sage Accpac 5.4 - we pay our sales reps commission on Margin.

We have 4 commission rates set up.  The reps are all set up with the correct commission rates in order entry.  The inventory categories are all set up with a 0% commission rate. 

The sales numbers and margins are all correct.  The commission report matches the sales history report Sales and Margin.  The commission report is calculating rates 1,2,3 correctly but is short on rate 4.

Does anyone have any idea what could be causing this?  Of course it is our year end and I need to balance these numbers.