Really hoping one of you fine people can help me as I am running out of hair to tear out.

My FSX/A install started misbehaving last night so it seemed the sensible option was to uninstall and then reinstall (I've done this before with no issues), so I went through the long process of carefully uninstalling absolutely anything FSX related, including the Acceleration SDK but not the main SDK for which I could find no uninstall option. When this was done in went DVD #1, it whirred away starting the install process and then up popped this notification

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which surprised me as I thought I'd uninstalled all the applications, so cannot for the life of me work out what it is trying to uninstall. Then after a couple of minutes I got

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I asked my old friend Google about the 1603 error and he gave me a few useful places to look, which gave me things to do. All of which I have done, I've cleaned the registry very thoroughly, I've run the resetsldl tool, I've defragged/optimised my drive, I've done everything I can think of and still end up with the same error messages.

So does anybody know how I can did myself out of this very annoying hole? Oh, worth mentioning, I had previously installed this in the C: drive root & was trying to do so again. HELP!!