Updating MinStock for a specific warehouse using DTW

I have found similar discussions, but can't find an answer. Using DTW, I want to update the MinStock value for a number of items, but for just a specific warehouse. The items are set to Manage Inventory by Warehouse. I have no problem when I update with LineNum in my OITW template, but when I use WhsCode instead of LineNum, I receive the following error from DTW: This entry already exists in the following tables (ODBC - 2035) Application-defined or object-defined error65171. Can't I update this based on WhsCode? I don't want to use LineNum because I don't think I can gaurantee that the LineNum, for the Warehouse I want to update, will always be the same. I don't want to ask the users to maintain a list of items and the appropriate LineNums associated with the specific Warehouse.

I would like something like this...

ParentKey   WarehouseCode     MinimalStock

ItemCode     WhsCode              MinStock

00000136     621sto                  12345

00000137     621sto                  98765

Rather than something like this...

ParentKey    LineNum     MinimalStock

ItemCode      LineNum     MinStock

00000136      7                12345

00000137      6                98765

Is this possible? I have tried with and without including OITM in the data source (with OITW). I have tried the 'Updating Existing Data' option and the 'Add New Data and Update Existing Data' option.

Thanks for any help and let me know if you would like more details.