No mapping data was returned from the server after

Went to http://weblogs.asp.net/scottgu/archive/2013/02/18/announcing-release-of-asp-net-and-web-tools-2012-2-update.aspx, downloaded and successfully installed the update but now when I try to view my site in page inspector it tells me "No mapping data was returned from the server". Created a new MVC4 app, and in that project page inspector works fine. I made sure Web Essentials 2012 extension was updated to the latest version prio to installing the 2012.2 update like the blog says. Also this page wasn't much of any help: http://msdn.microsoft.com/en-us/library/jj204395.aspx: Error No mapping data was returned from the server Description Page Inspector can’t map between the browser and source code. Cause Not determined. Fix No specific recommendations.

Any idea what could be wrong and what else I should try?

Edit: This is superweird. I did absolutely nothing and now all of the sudden it works again! Unless closing and opening Visual Studio and the project a couple of times counts. This is how it looks now - notice the difference in the first and last bullet:

Edit2: Used IISExpress in both projects. "No mapping data was returned from the server". Sounds like it could be an issue with IISExpress not liking the new stuff that where installed?

Edit3: This piece of code breaks page inspector:

<map id="surfer" name="surfer">
   <area shape="poly" coords="0,23,30,13,40,3,64,5,69,19,86,23,98,30,99,51,72,63,68,83,41,83,38,67,1,65" alt="&%#&#064;?!">
</map>

Never thought that it could actually break an entire tool so didn't bother to test. Here's where I got the tip: http://social.msdn.microsoft.com/Forums/sv/visualstudiogeneral/thread/470ece78-86c3-4fab-b38c-cb969d515d43

Seems like a bug in page inspector/razor engine or in both.

Caused by a bug in page inspector/razor engine. Will get fixed soon. See Anands comment in question.