After I installed VS11 Dev Preview, VS2010 cannot start debugging the Sharepoint 2010 server (developer install on Windows 7). I get a nice error dialog stating:

Unable to start debugging on the web server. The debugger is not properly installed. Cannot debug the requested type of code. Run setup to install or repair the debugger.

Click Help for more information.

The message in the Output Window (Debug) says:

Auto-attach to process '[9808] w3wp.exe' on machine 'LT01529' failed. The debugger is not properly installed. Cannot debug the requested type of code. Run setup to install or repair the debugger.

Start debugging did however work from VS11. I have now uninstalled VS11, and repaired my VS2010 installation, but the problem persists.

What does work, is to 'Attach to process'. Then debugging works correctly (breakpoints, stepping, etc).

From the native stack (attached to devenv with another instance), it appears there is some invalid COM cast.

Anybody have ideas how to solve this?




It appears VS11 overwrote files in VS7Debug (Common files/ms shared), that are left over even after uninstall. I assume getting the VS2010 versions should fix the issue.

Update 2:

The above did not work.

  • 1
    Could it be anything to do with this?
    – CraigTP
    Nov 4, 2011 at 9:39
  • Uninstalled 4.5, same results. Uninstalling and reinstalling VS2010 now due it breaking after uninstalling 4.5 :(
    – leppie
    Nov 4, 2011 at 11:15
  • Did the re-install work? Nov 13, 2011 at 15:00
  • Nope. Many things still broken. Looks like a complete OS re-install is the way forward.
    – leppie
    Nov 13, 2011 at 15:37
  • 1
    I had the same issue when I uninstalled Dev11. When I started getting the error, I completely uninstalled VS, wiping away any remaining files (but not messing with the Registry.) That did not work! So I have been manually attaching the debugger every time I F5. It was a PITA to start but after a couple of months, i've just gotten used to it! It's time to build a new Dev VM anyway. I guess this is what I get for installing the Dev Preview on my primary Dev VM. I seem to remember ignoring some warning about "Pre-Beta yada yada yada." LOL I'd love to know the answer, just to learn something. Dec 16, 2011 at 21:17

2 Answers 2


This is why i only work from VM's, they're easily replaced, and my host OS (Server 2008R2) remains clean and fast. I have a whole domain running in multiple VM's and only have the bare minimum installed directly on my laptop (Only Office basically). Whenever a new version of a product is released, i create a new VM and test / try it in there. If it breaks, no worries.

  • 1
    Virtualising is much easier and more mature now, it is the way to go for SharePoint dev in general.
    – Russell
    Dec 23, 2011 at 9:23
  • -1: not really an answer... Apr 24, 2012 at 11:41
  • Yet most people agree, especially regarding installation of Beta (or even Alpha) software.
    – Colin
    May 1, 2012 at 8:40

This seems to have started working again after installing VS2012 RC.

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