By the looks of it, I feel that the problem is with the SPARQL query itself. Although, I'm aware that the query is syntactically correct and conforms to the SPARQL specifications, I wonder whether the Apache Jena version used in DSS allows you to follow the syntax "INSERT DATA" (just a wild guess analyzing the reported error log). Can you try "INSERT (INTO)" clause and check if it works? Ideally, DSS doesn't do any modifications to the query except input/output mapping processing so if your query format is right it should work out of the box.
Cheers, Prabath