Hmmm...
I can connect in SQL Plus so I don't think it's SQL net...
Funny I get a blank error? I have an idea to check the PATHS for previous Oracle crap on both these PC's oracle has been installed several times in different home. Perhaps it is something on Oracle? I'll check the reg keys.

>Then the problem is probably not the drivers. Make sure the SQLNet client is configured correctly. Make sure the registry keys for Oracle are corretly pointing to where SQL Net is installed. If all else fails, try reinstalling the SQL Net client.