I am similarly unable to reach a remote Oracle database configured as a service, when through SQL Developer I can. I have a valid tsnames.ora with both the PATH set to the InstantClient directory, and TNS_ADMIN pointing to the location for tsnames.ora (SQL Developer picks up the service information from tsnames.ora successfully, and did not before TNS_ADMIN had the correct value.)
I *am* having exactly the same access problem with another Eclipse-based client tool.
Glad to assist with diagnostics. Looking for guidance on what to go after.
Thanks,
jbullock