Although most software installers register their own files, the process of uninstalling software and upgrading operating systems can leave your computer with files that are unregistered with the system. The "MSCOMCTL.OCX" file normally resides in your system library and must be registered with the system in order to be properly used. If for any reason you have an application that gives you a MSCOMCTL.OCX error, you'll need to reregister the file in order to make your software work. Registering a file is a quick process, but you will need administrative rights to perform it.
Download the MSCOMCTL.OCX file if you do not have it (see Resources).
Open the downloaded file and extract it using your preferred archive management program. Place it in the "C:\WINDOWS\SYSTEM32" folder.
Click Start and select "Run" if you are using Windows 2003 or XP. For Windows Vista and later, click in the text input bar on the Start menu.
Enter the text "REGSVR32 MSCOMCTL.OCX".
Click "Yes" if you are requested to give "REGSVR32.EXE" administrative rights. You have now registered MSCOMCTL.OCX with the system.