The listener received a request to establish a connection to a database or other service. The connect descriptor received by the listener specified a service name for a service (usually a database service) that either has not yet dynamically registered with the listener or has not been statically configured for the listener. This may be a temporary condition such as after the listener has started, but before the database instance has registered with the listener.
When you launch Subset from within Datamaker, you are seeing the error because it is expecting the "tnsnames.ora" file in the Datamaker installation folder.
You will see this error if you do not have the TNSNAMES.ORA files in these locations with the instance and service names listed correctly:
C:\Program Files (x86)\Grid-Tools\GTDatamaker
Make sure the profiles that are stored in %APPDATA%\Grid-Tools\profiles.xml are accurate.
You can also use the Utilities -> Connect Repository menu option to make sure you select the right profile for the repository connection, which would update the profiles.xml file.