Enter Sales Credits from the Auto Invoice Interface Lines form

Dear Friends,

One of the invoices is stuck in the interface with the below mentioned error:

You must supply sales credit assignments for this transaction because the system option Require Salesreps is set to Yes

I understand that this error is because of missing records in RA_INTERFACE_SALESCREDITS_ALL table.

Now, i am trying enter sales credits data from the Autoinvoice Interface lines form.

I am providing values to the following columns but it says that the line already exists and i am providing duplicate sequence of values.

Could any one please tell why i am getting this error?