Couldn't get write access to the "HKEY_CLASSES_ROOT... error message during installation:

To solve the problem you have to go to your registry by using "regedit". Then located ".pcx" (or any other key you get the error message for like .jpg, .tif and etc...) registry entry, right click on it and select permissions, then change the permission to "allow" "full control" and "read" for your username, then reinstall the application , this time it should work successfully.