Selecting the 32 or 64 bit version
The ClearContext installer normally detects whether the 32 or 64 bit version of Outlook is installed, and will automatically select the matching ClearContext version. In the rare case where one has to manually select the version, the 32/64 bitness of ClearContext needs to match the 32/64 bitness of Outlook. You can verify whether your Outlook is 32 or 64 bits by going to the Outlook File->Office Account->About Outlook screen (may vary by version). By the full version number there will be a 32 or 64 bit label.
When ClearContext is installed - in the Programs section of the Windows Control Panel, the 64 bit version of ClearContext will be listed as a 64 bit version, while the 32 bit version has no bitness description.
Note for older versions:
In older versions of ClearContext, the 32 or 64 bit installer needed to be manually selected and used. The Outlook version should be checked as described above to to select the correct version. Occasionally, the installer may incorrectly warn about the wrong version, and if you have verified the correct version, you can be override the warning and proceed with installation.
If the 32/64 bit version needs to be switched, be sure to first shut down Outlook and uninstall ClearContext through the Windows Control Panel before installing a different version.