Here's one approach.

Do you have a sqlnet.ora file anywhere on your client?

If so, look for the parameter NAMES.DIRECTORY_PATH

It may look something like this: NAMES.DIRECTORY_PATH=(tnsnames, ldap)

It specifies what to use for name (connection info) resolution and in what order to use it.

It might be helpful to run netca and netmgr and see what Oracle think's it's got - that is, if you don't want to do a manual configuration of name resolution.

Sucks, don't it. This could be made a ton easier.