How do I get my Jscript Debugger to Attach to a Process?

I get the following JScript Debugger error when I click on the Start Debugging button in the Script tab of the Developer Tools (F12) window:

Unable to attach to the process. Another debugger might be attached to the process.

1. Closing all browser windows and launching ie again has no effect.
2. Ending the process tree in Windows Task Manager and starting a new iexplore task has no effect.
3. Hitting Shift-F5 when in the Developer Tools window has no effect.
4. Rebooting the entire machine reveals how desperate I am and has no effect.
5. Searching in Regedit's [HKEY_LOCAL_MACHINE\SOFTWARE]开发者_StackOverflow中文版 branch for "JITDebug" just reveals I don't know what the hell I'm looking for.

• I find that I experience this problem when launching a site in debug mode from Visual Studio.
• If you would like to use the debugger in Internet Explorer Developer Tools you would need to launch the site outside of Visual Studio.