When attempting an installation of QCS (Quest Collaboration Services), you may receive a "Class Not Registered" error.
Internet Information Server (IIS) is installed on the same computer that QCS is being installed on.
Antivirus may also be the cause of this issue.
Install the IIS 6.0 Management Compatibility Components and re-install QCS.
**NOTE*** If you are installing QCS 3.7 on Windows 2012 you will need to install the IIS 6.0 Management Compatibility Components.
Remove IIS from the computer and re-install QCS.
Disable Antivirus software on the QCS server and re-install QCS.
AntiVirus programs often implement complex protection mechanisms and may sometimes still be engaged even when you believe they have been disabled. There may be multiple pieces that need to be turned off and often more than one service helping to protect them from circumventing the protection.
You may even have to try uninstalling the Antivirus software if you are unsure of how to completely disable the software.