Please note: If you are using a non-Comcast version of PhotoShow 4 or earlier on Vista, it will not work.
With that said...
You can try the solution below however, you will loose the Shows saved to your program.
Uninstall the program. During the uninstall process uncheck the box asking you to keep the PhotoShow database. Then reinstall PhotoShow.
You can download your shows from your site back into your program after the new install.
If this does not help, contact support.