The above example exception notes AS400JDBCConnection, however this could occur with any supported data source, such as:
The JDBC driver is outdated and as such it implemented Java 1.6's
Reference the supported data source documentation.
If the driver is not provided with Test Data Manager (TDM), then upgrade the JDBC driver accordingly and/or contact the vendor of the JDBC driver if there are any questions about the implementation of specific methods, such as isValid().
While a highly unlikely scenario, if the driver is provided with TDM, please open a case with Support, so we can assist you accordingly.