I am running progress billings from NAV and I have come across a few jobs where the contract amount does not populate on the invoice.  Everything (i.e. invoice amount, past amounts billed) calculates properly except amount remaining which is a negative number.  I could fix off-line, but would rather have the system process the invoice properly.   This has not happened on many jobs, but enough that I am seeing a pattern.  

Does anyone know what would cause the contract amount not to populate on the Progress Invoice?  Is it a setup issue?  Something else?