You need to alter your permissions in windows. For some reason i have found that certain versions of windows lock the files to administrator rights only. If you have user accounts set up on your machine you will need to be running under one of the admin ones to alter the files.
Also make sure that no other instances of the program are running at the same time as that can cause the issue too, but to be honest it sounds more like an admin rights issue.
Hope that helps. Feel free to message or email me if it doesn't and i will try to help more if i can.