Error connecting to database: "ORA-12571: TNS:packet writer failure." (4221242)

The following error occurs when connecting to database:
ORA-12571: TNS:packet writer failure.

Connection can be established using other applications such as Toad for Oracle.

1. Start | Control Panel | System
2. Advanced Tab | Environment Variables
3. Under System Variables list, scroll down to Path and select Edit
4. Move the BIN folder of the Oracle Home to the first path listed on the list of paths. This path is where OCI.DLL file resides
5. Under System Variables list, scroll down to TNS_ADMIN Path and select Edit or select New if not found
6. Ensure the ADMIN\Network path exists in the Value field of the variable. This path is where the TNSNames.ora file resides
7. Close and reopen Optimizer and ensure the specified client is selected under Connect Using drop and down and connect