Did you change any of the driver property (--property of connection pool). If you do so after deploying the application that is accessing the pool, you will have to redeploy the application or restart glassfish.
http://docs.sun.com/app/docs/doc/819-3671/ablch?a=view
If you are facing the issue straight away (start appserver, application's fresh access gets the exception),
can you post the server.log (with "connectors" and "resource-adapter" log-levels set to FINEST) ?
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