When trying to run the upgraded version, that cryptic popup message generally means the drive/location of iTunes can't be found. Follow these quick/short instructions to check drive management, first (start by performing a "warm" boot, or "Restart"):
After your system is ready and you've logged in with "Administrator's" Permission Hold the key down and press the key. This opens up your quick Run box - you can run most any program from there. Type the following into the input box that's presented to you, then hit :
This will directly up the "Disk Management" snap in, where many different options can be made to your various drives.
Look over status of your drive management system, to see that your drives are as they should be. You can also double-click (Left Mouse Button) on which the drive where iTunes is installed; this is just to verify the path to and all files for iTunes are as they should be. Double-click iTunes.exe - should be found in the path (based on the default installation on Drive C:), to verify that it runs without the error popup.
Close out of everything you've opened that may still be open when you are done.
The next easy option is simply to Open your Control Panel, then double-click on the icon entitled "Programs and Features." When fully loaded and open you'll see a long listing of all installed Programs and files. Find the iTunes entry and double-click to uninstall; once completed, you should perform a Reboot and unplug the system's power cord completely, leaving it OFF for at least 15-30 secs (this helps to ensure that all memory is 100% blank, without any residual bits/bytes of code/data left behind that could possibly cause sporadic problems later on (which is what occurs with a Restart or "Warm" boot).
Reboot once more, then when your logged back in with "administrator's" Permission, turn OFF your AV, malware protection and firewall (don't be scared - as AV programs are becoming more entwined into the opsys, it's prudent to
turn it off, just before installing and turning on immediately after). Lastly, you could try installing in "Safe" mode. I hope this is of some help!