Can you provide samples of the data that you are populating the staging tables with that cause the error?  That would help in trying to determine what the issue may be.

Attached below are the lines for the order in the staging table

Line samples.xlsx

Are these Items Kits?  Within timItem, the ItemType will be 7 or 8 if they are.  If not, have you tried processing one of the problem records and doing a SQL trace to see where that error may be getting logged at?

If they are kits, you will need to include the components for them as well and set the kit component flag to 1 in stgSOLine.