This error may occur when adjusting a Gift Transaction that has a ST (stock) Payment Method from Transaction Type GF to PP. The status of the stock gift item (which can be viewed by zooming in on the ST Payment Method in Batch Detail) gets changed from 'N' (no change) to 'I' (Insert) when the Transaction type is changed from GF to PP in the adjustment batch. This causes TA to try and insert the same stock gift item with the same Stock_Seq again, which causes an error.
The workaround is to change the Status of the batch stock gift item from 'I' back to 'N'. This cannot be done from TA front end, so contact TA support for assistance.