It's been quite a while since I use Sun Java System App Server 8. If I'm not wrong, you can go to the admin console->Application Server->In the General tab, click on the JDNI Browsing button. Make sure your JNDI is there. If not, then there must be something wrong with it.
SCJP 5.0, SCWCD 1.4, SCBCD 1.3, SCDJWS 1.4
subject: How to look up the JNDI in Aun App server (version 8)