Who knew that about.com could be useful? I've recently been working with Rails on Oracle 8i and ran across a problem when I updated my client to support a 10g database. The error was:
ORA-12705: Cannot access NLS data files or invalid environment specified
I found the solution at ruby.about.com:
Another common problem is interference with a current or prior Oracle client install. The error "ORA-12705: Cannot access NLS data files or invalid environment specified" usually occurs because of an incorrect NLS_LANG setting. Unix users can just unset NLS_LANG but Windows users will need to modify their registry using regedt32 and remove the NLS_LANG key in the following location.\HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\
Everything worked just fine as soon as I went into regedit and deleted the NLS_LANG key. Hooray!