JDBC Adapter Connection but Adapter Service Fails


We are having an issue retrieving information from a database using JDBC Adapter version 6.5 running on IS We are able to successfully enable a connection from the JDBC connections page on the web UI, but when we attempt to run a simple select statement from an Adapter Service in Developer we receive the below error:

We are able to reload values from the adapter in the adapter service, view the tables, and set everything up successfully, however when we run the service to test we get the error.

The database is located on another network and we are connecting through a VPN tunnel. We have verified the connectivity: we can ping the server on the listening port and we can perform the exact SELECT statement configured in the Adapter Service using SQL*Plus client from the server IS is running on. I have tried many different configurations, but have no luck.

Here are our connection details:

Any help is greatly appreciated!