Re: New object "CAD Part - XXXXXX.prt" has the same filename that already exists in the database in a restricted context. In order to upload this object, you must update this object in the workspace.

Basically, you already have something else in Windchill using this name.  You can either rename the new object to something different or "Update" the new object to become the next iteration of the already existing object.  If you decide to update, you will also need to check out (and possibly revise) after updating.