In some versions starting with 2.2.0, the iCap installer opens up a DOS window that registers the software serial port (Eltima) DLL. This DOS window stays open for a long time with no output before it completes running. You MUST leave this window on your screen until it closes by itself to properly install the iCap software serial port module.
If you return to the installer and click "repair", you should be able to try again and no longer have this problem.
This should be fixed in future versions of the iCap installer.