It is most likely caused by Windows itself. Windows (especially Windows 10) will prevent VBScript from writing to most parts of the file system. It does allow VBScript to write to the Desktop or any other folder under Users. This isn't an issue with UFT, but with Windows and how it handles VBScript permissions. You can try this for yourself by the following test script. Just change the part to one of the Windows user ids on your machine. You can navigate to the C:Users path to get that if you need. The sample code should run and create a small test file on the user's desktop. You can also change the Desktop to be something like Downloads, Documents, etc. as long as it is a folder under the user.
Set FS=FSO.CreateTextFile(''C:UsersDesktopTest.txt'', True)
FS.WriteLine ''This is a test''