Auto Invoice error

Hi

1)I have created an order and shipped items to the customer. 

2)A return order is booked returning part of the quantity.

3)All the lines have been transferred to RA interface table

4)Run auto invoice

It got errored for the lines

Errors:   1) This line has the same transaction flexfield as another row in the interface table.  For each transaction line, the
               combination of interface_line_context and interface_line_attribute values must be unique. (59)

Following are the flex field combinations

Invoice
-------
Transaction Flexfield: ORDER ENTRY: 57.SV Order Type1.3969373.0.0.401478.0.0.0.14806.0.1.0.0>>Item
Transaction Flexfield: ORDER ENTRY: 57.SV Order Type1.3969373.0.1.3945388.0.0.0.14806.0.0.0.0>>Freight

Credit memo