Are you sure your antiviiral or your anti-malware software isn't the culprit here?   "A digital signature is an electronic security mark that can be added to files. It allows you to verify the publisher of a file and helps verify that the file has not changed since it was digitally signed. " You may want to uninstall and reinstall whatever security software you're using (eg, Norton, McAfee, etc). Your system restore may have deleted/corrupted the security software's database of valid digital signatures so it's just decided that "whatever" is unsafe and it's not  going to let you install it.  Ron
I have an XPS210 Windows Vista Home Premium. I did a system restore on 7/31/09 and has had problems ever since. I am able to get the automatic updates but I can't go anyother websites to download and install files. Unverifiable digital signature. If I save it to my desktop and run as an Admin windows causes the program to stop running.   Please someone help me !!!!!!!!!! This problem has stumped Microsoft and Dell Tech support
Windows Vista Clean Install errors