From: <glassfish_at_javadesktop.org>
Date: Sun, 22 Mar 2009 22:27:39 PDT

you can set the "module-log-level" of "connector" to "FINEST" (via GUI / CLI) and see the root cause.
It seems like appserver is unable to create the physical connection.

eg:
asadmin set server.log-service.module-log-levels.connector=FINEST
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http://forums.java.net/jive/thread.jspa?messageID=338407