I've found a remedy to this error.
If you add
RETURN BO
to the end of the action there is no "Internal Error" and the SQL is successfully executed. So
EXEC_SQL `UPDATE CRM_Customer SET Name='John'` RETURN AnyBO
works ok. (replacing CRM_Customer, Name and AnyBO with a real Business Object)
Seems AwareIM just wants to see this
RETURN AnyBo
at the end of the command even though it does not return anything related to "AnyBo".
This EXEC_SQL is powerful but as Vlad warns
to be careful when using this acton as you can stuff up your database