If the hosts could no be reached, it would give a different exception (I'd say). Of course, the connection
string can (and should!) be verified using TNSPING.
I've never heard of the
NL Exception, but a cursory search on the net shows it is a wild beast. I'll move this question to our Oracle forum, where our Oracle folks hang out.
Also, ojdbc5.jar comes in different versions. You might try to
download the most recent one.