I had un-installed AVG8.5, using AVG's un-installer, and installed Microsoft Security Essentials, on a WinXP Pro PC, seemingly all going okay. When I stopped MSE working, to run a defrag programme, Windows objected and warned me that I had multiple anti-virus programmes loaded, but that none were in operation.
I followed the instructions in your link and Windows is now convinced that only one anti-virus programme is loaded.
Thanks again, Peter.
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