I would suggest that you recheck your tnsnames.ora file again and make suer that the listeners are up and running.

03505, 00000, "Failed to resolve name"
// *Cause: The service name you provided could not be found in TNSNAMES.ORA, an Oracle Names server, or a native naming service.
// *Action: Verify that you entered the service name correctly. You may need to ensure that the name was entered correctly into the network configuration.


Also check your sqlnet.ora and make suer that the resolution methods are mentioned and if there any domain name extension, then you have to use it on your service name under tnsnames.ora file.

Sam