A new version of Transformation API was released today with a new feature - we're blocking all SELECT queries.
These queries do not perform any real operation to your data (if not accompanied with CREATE TABLE or CREATE VIEW) and caused our servers to load the result in memory. If your transformation contains a pure SELECT query, it will fail with a Query not valid error message.
The fix is easy - delete or comment the SELECT query, it won't effect your transformation.
Thanks for your understanding.