Have you tried right-clicking on the shortcut to the program, or the .exe, and selecting the "Run As Administrator" option? Do so even if your user is an Admin.
If you decide a reinstall is in order try right-clicking on the actual Setup.exe and selecting the "Run As Administrator" option? Do so even if your user is an Admin.
Have you tried cleaning out your Temp folder, you can do it by typing %temp% in the RUN box. Accessed via Windows Key + R. This will open your Temp folder, there you can delete everything that Windows will allow you to do so.
It may be necessary to show both Hidden, and System Files, and also to uncheck "Hide known file types" in Control Panel/ Folder Options/ View, to navigate to, and see all files in, the mentioned Temp location.
Is the Temp folder that opens when you use %temp% the same one as ""C:\Users\MYNAME~1\AppData\Local\Temp", or is it opening another user's Temp folder? In other words is "MYNAME~1" the user you are logged on with?
Does your program work if you test with another user rather than the current user?
Create a user account Windows 8.1
http://windows.microsoft.com/en-au/windows/create-user-account#create-user-account=windows-8