How to populate a sourced field beforeSubmit

I have a parent-child sourced field on the transaction record back to the customer record so I can list transactions (different reason than the standard transaction list on the customer record).

When a customers name is set manually in the transaction, it takes no problem and links the two. However when I try to do this using SuiteScript I get an unexpected error. Oddly, it does not get caught in my try/catch and does not show up in my execution log (nor emails us).

Am I doing something wrong? I'm doing this on beforeSubmit() from an online sales order form. Is there an issue with sourcing customer records from the customer center (customer can not see?)? Snippet of code is below (nlapiGetNewRecord has already been called previously. csiError and csiWriteToErrorLog ar emy library files -- they work. custbody_pcust_customerlink is the sourced field that links customer to transactions):