I Installed Oracle Client32Bit on Windows 2008 R2 64Bit. When I was trying to connect through TOAD it was giving an error ORA-06413 Connection Not Open on the same system. Cause: TOAD Was installed in Program Files (86) Solution: I installed TOAD into QUEST folder in C: drive. Note : The similar problem was coming with .Net application also in establishing connection with Oracle. So, I suggested to install .Net in other folder not in default location "Program Files(86)".