The VHD base that I use for building Virtual Machine images for Windows 7 comes with the Kernel Debugger enabled. With the Kernel Debugger enabled you cannot start the Visual Studio 2010 debugger. Here's how I had to remove it. You can't just edit BOOT.INI any longer since these parameters are stored elsewhere and a new tool BCDEDIT.EXE must be used.
Start an administrative command prompt.
BCDEDIT /debug OFF
It will say the operation completed successfully. Now reboot and then start Visual Studio 2010 again.