This error can occur when the driver name specified in the UI cannot be found. Review the JDBC Driver Class Name in the Legacy Drivers tab (show Advanced Options → Legacy Drivers). And review whether the driver is correctly installed. This field should only be filled in when the JDBC driver is not compliant with the JDBC 4 spec. Most popular drivers currently implement the JDBC 4 specification, so the JDBC Driver Class Name field does not have to be filled out. Some of the drivers that support JDBC 4 are MySQL, Postgres, Oracle.