“unable to start debugging on the web server” MSVSMON.EXE failed to start. VS2010 error

having a real problem getting VS2010 to debug IIS.

I've searched on the internet for a few days now and tried every single solution I can. VS2008 works perfectly but I've installed VS2010 and when trying to debug an IIS site (by pressing F5 on a project that uses IIS) I get the error message

"unable to start debugging on the web server. Microsoft Visual Studio Debugging Monitor (MSVSMON.EXE) failed to start. If this problem persists, please repair your Visual installation via "add or remove programs" in the control panel."

when i try attaching the process manually, i get the same message.
I've tried repairing the software. I tried it, it failed, so I uninstalled using the Microsoft Visual Studio 2010 Uninstall Utility (http://archive.msdn.microsoft.com/vs2010uninstall/Release/ProjectReleases.aspx?ReleaseId=4321), then reinstalled and it still has the same problem. With the SP1 update this still happens. I can run the website fine when running "start without debugging" and it runs fine.

I've gone through all the guides I can and all tried all the settings on IIS I can and still no luck. I'm using Windows 7 64bit if that means anything. I can detail much more about all the things i've tried.

also have a laptop and have done the same, installing VS2010 and TFS (also on win7 64bit), and this works perfectly for debugging. Didn't have to mess around at all. I can't see any difference between this and my PC with the problem. I'm scratching my head here and thinking I might have to format my PC and try again from a fresh install (which would be seriously annoying!)

Thanks to anyone that reads this,
Dan Gent