Invalid Invoice Type error During AR Invoice Entry

We just updated from 8.03.403d to 409c and are now getting an error we didn't used to get.

In AR Invoice entry, After selecting a packer using "Get Shipments", we get an error if we change the Unit Price or Product Group. The error states, "Invaid Invoice type", with error details as follows:

Error Detail
Message: Invalid invoice type.
Type: Error
Program: bo/ARInvoice.p
Method: validatePartDesc
Table: ttInvcHead
Field: InvoiceType

If we don't have to change the unit price it is just fine.

Any thoughts?