See this blog in the issue. It basiclly says to make sure "show all files" is selected in the solution and check for any folders that don't belong that are not part of your project/solution.
The problem resurfaced again a few days later and I finally figured out the problem with my uncooperative debugger. I have a folder containing approximately 20,000 images that are not included in the Visual Studio web project but are sitting in a directory in the web site. I had turned on "Show All Files" in Solution Explorer to add some script files into the project. When "Show All Files" is off, F5 (Start Debugging) works like champ. When "Show All Files" is on, Visual Studio becomes unresponsive. In reality it is not "frozen" but simply taking a very long time to process those 20,000 image files.
For me, it was a folder created called backup
, which was a backup of the site (created by VS). I deleted the folder in question and the site loaded for debugging.