I started having this problem with one of my applications that connects to a WCF service I was debugging at home.  Plenty of posts exist telling you to make sure there is a <system.web><compilation debug=”true:” /></system.web> entry in your web.config. 

Well for most people that works but I learned that trick 9 years ago when Web Services first came on the scene.  This was clearly different.

As it turns out the problem is related to the x64 debugging toolset (or the lack-thereof in Visual Studio 2008 et al).

The solution was simple.  In the consuming application change the target CPU from Any CPU or x64 to x86.

Bad setting:

Good Setting:

Now you can step into your WCF service.  Also, you should start campaigning to get a 64 bit version of Visual Studio 2010…etc.  Microsoft’s Visual Studio development teams seems to think that it is an unnecessary feature.  I beg to differ.