Have you confirmed that that is the correct JNDI name?
Different app.servers use different naming conventions (sigh), and I believe that GF uses the java:comp/ convention (I think it's comp/env but not entirely sure).
You can browse the JNDI tree from the GF admin screen; on the main page there's a JNDI Browser button at the top of the RH pane.
[Message sent by forum member 'matterbury' (matterbury)]
http://forums.java.net/jive/thread.jspa?messageID=353813