The fact that you can't get UTAU to run from your Documents folder means that there seems to be some NTFS permissions going on since it is your user and it supposed to allow you to run anything from there.
It seems that Windows messed up its security settings. Have you tried making a new account to see if it still encounters the same problem? You may need to reset the security permissions on the computer, or maybe change the UAC settings for the user (though I doubt that'll solve the issue) but let's try simpler methods first.
It seems that Windows messed up its security settings. Have you tried making a new account to see if it still encounters the same problem? You may need to reset the security permissions on the computer, or maybe change the UAC settings for the user (though I doubt that'll solve the issue) but let's try simpler methods first.