NAST Update Failure

on save of the sales order for an output type, I need to get all the contact person for the customer. for each contact person based on his communication preference an output record should be added into NAST.

A program is configured in NAST which will be triggered for my specific output type. Here I am trying to insert records into NAST and doing a submit RSNAST00 program. Once this is done in update mode in a new task, I am getting the error the object is blocked by my user ID.

Is there a way to release the locks? or a better approach is to find an user exit? I am not finding a place where NAST table is being filled in an user exit to insert a new output record.

Thanks,

Karthik