Before you do any changing of programs whether it be installing, re installing or uninstalling, you'll want to make sure you have full access to all files on your system. This means that you'll have to go in to Control Panel (Control Panel\User Accounts\User Accounts if you're using Windows 7) and Change User Account Control settings to "Never Notify".
Microvellum Software needs access to registry settings and sometimes downloaded content is blocked by your system. To change this setting, right-click over the downloaded file and click on "Properties". At the bottom of the splash screen, select the "Unblock" toggle:
Now extract all the folders contents.
Once you've done that, then find the setup.exe, right-click on it, and select "Run as Administrator" (if using Windows 7):
Proceed with installation: