In 2010 (wow! that’s a long time ago…) I blogged about how to debug Blend design time exceptions, since then things have changed, Blend and Visual studio designer merged and so the XAML designer is now hosted in a separate process named XDesProc.exe (at least in Windows Store applications)
Laurent Bugnion has a detailed blog post about how to attach Visual Studio debugger to Blend to debug a Windows Store application at design time so i won’t repeat it here, the reason of this post is to integrate it with another step required when you use Visual Studio 2013 and Blend 2013.
Since with latest release PDB are no longer copied to cache location used by designer your simbols won’t be loaded and your attach procedure won’t work.
The solution is very easy, just point the debugger symbols to the proper PDB files of your application and everything will work as expected.
To point the PDBs just use: Tools –> Options-> Debugger
Then add the folder where your app’s PDB file resides.