If what Zubaz suggests doesn't works, refresh your XML data under tools. If that doesn't work, uninstall SDC, run a clean up program like CCleaner reboot and reinstall SDC. It could be just a bad download of SDC.
Since you are on Vista make sure you are running in Admin mode or with Admin privliges. I don't run Vista so not sure what it is called.
Worth trying if you haven't all ready done so.