When I start/launch Toad and try to connect, I get the error: "System.InvalidCastException Unable (4309293)

After launching or starting Toad and trying to connect to an Oracle database, I get the following error. After clicking on the OK button, the errorappears again. This error may have started happening after I uninstalled / resintalled my Microsoft .Net Framework 3.0 and/or 3.5.

System.InvalidCastException
Unable to cast object of type Quest.Toad.Oracle.DBMS.DBMSOutputSettings to type Quest.Toad.Oracle.OracleSettings.
Stack Trace:
at Quest.Toad.Oracle.OracleSettings.get_Instance()
at Quest.Toad.Oracle.OracleToadConnection..ctor(OracleProvider connectionProvider, OracleConnectionMediator mediator)

I have tried uninstallingand reinstalling my Toad, but with no success in resolving the error.