The TNSNames.ora Editor plug-in isn't referencing the TNS_ADMIN system environment variable. Instead, it's locating the tnsnames.ora file located in the \network\admin directory.

On my machine, TNS_ADMIN points to c:\oracle\admin. The plug-in isn't using the tnsnames.ora file in this location, although both Oracle and PL/SQL Developer do. Instead, it's using the tnsnames.ora file located in C:\oracle\product\10.2.0\client_1\NETWORK\ADMIN.

I have forwarded this to the author.

Thanks for the feedback, the TNS_ADMIN envar is (AFAIK) optional & if not specified defaults to ORACLE_HOME\network\admin. I have now modified the plugin to check the TNS_ADMIN envar.
I have uploaded it to my webspace -
http://milagro.pwp.blueyonder.co.uk/downloads/TNSEditorPlugin.zip
Could Marco reload it onto the main website download area ?

Thanks.