When attempting to switch SQL Optimizer versions in the Version Selector (Start | Programs | Quest Software | Quest SQL Optimizer for Oracle | SQL Optimizer Version Selector), the option for Version 7 is greyed out as it's unable to locate the file QPRBv7.dll in the specified directory.
This occurs on non-English Windows Operating Systems.
By default, the version selector looks for the directory:
C:\Program Files\Common Files\Quest Shared\Quest SQL Optimizer Shared\QPRBv7.dll
However, in reality, the dll exists in the following location:
C:\Programme\Gemeinsame Dateien\Quest Shared\Quest SQL Optimizer Shared\QPRBv7.dll
Manually create the directory 'C:\Program Files\Common Files\Quest Shared\Quest SQL Optimizer Shared\' and copy the QPRBv7.dll to this new location.