Write GP Results to Feature Class

Hello

I would like to write the results of a Buffer operation on Feature Class A to an existing Feature Class B where both A and B are on SQL Server. Both A and B are also published as Feature Layers to ArcGIS Server. When I try to build a Model to do this I keep getting errors to do with the fact that the Feature Class B already exists and/or there is a conflict with already established locks on the database.

Is there a recommended approach to doing this?

Any advice appreciated.

Eamonn