I executed the similar SQL for truncating and inserting in my environment, but I successfully executed the SQL and I could not reproduce the error you are facing.
As we need more information to investigate the error, could you please open a support ticket by sending an email to email@example.com with your scenario’s diagnosis logs which can be downloaded by clicking the “Download diagnosis” link on the “Last runs” tab of the “Scenarios” page on DSS.
By the way, if your table is registered and managed as a dataset you can use the “Clear” step for clearing your table’s data instead of writing a TRUNCATE statement in the “Execute SQL” step. This way would make your scenario simpler. Could you elaborate your use case so that we can find other options to achieve your goals efficiently?