"ORA-03121 no interface driver connected - function not performed" Error When Connecting as Non A (4273391)

When connecting to TOAD as a non-administrator on a local PC, the following error is returned:

ORA-03121 no interface driver connected - function not performed.

Installing and connecting, as an administrator is successful.

RESOLUTION:
Normally a SQL*Net issue and not TOAD itself. Confirm that the user has the correct oracle client installed.

Things to check:
1) That the %ORACLE_HOME%\Bin environment variable is specified in the path.
2) Check the registry, make sure the user has the correct registry entries under HKLM | Software | Oracle.
3) Make sure the user has the read/write privileges on the ORACLE_HOME directory and all sub directories.

ORA-03121 no interface driver connected - function not performed

Cause: This message occurs usually because the Net8 driver is not loaded into memory or there is a mismatch of the version of the driver. A user program linked with an obsolete library may also cause this message. Only programs provided by Oracle Corporation should use this interface.

Action: If the message occurred during use of a program provided by Oracle Corporation, contact Oracle Support Services. If a user program caused the message, relink the program with current versions of the Oracle libraries.

TOAD requires a the SQL*Net to be properly configured as we utilize the OCI supplied by Oracle, if this is not properly configured for the user then you will get the above error.