With so many scanners, it might be that you have something that not many security software vendors have seen. It also could be a policy set by a system administrator (normal Windows functionality). Another possibility is that with all that security software running, it may be set to block changes to those key areas. I would suggest you try the changes in Safe Mode with most all of the security software disabled. If the problem persists, a more detailed description of the computer setup would be needed.
Operating System, If it's on a domain or not, any other symptoms, ect.
DETAILS are extremely important.
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