PRC: Distribute Usage and Miscellaneous Costs. error

 I am getting error pacgud: ORA-01400: cannot insert NULL into ("PA"."PA_COST_DISTRIBUTION_LINES_ALL"."AMOUNT") when running PRC: Distribute Usage and Miscellaneous Costs.

The expenditure item line was created prior using the Cost Collector Manager process that transfers records from the PA_TRANSACTION_INTERFACE_ALL. Which cost field can be missing - why am I getting this cannot insert NULL amount error??

Thanks.