There are times when you feel almost alone, particularly when you type an error code in google, and nothing comes up.
I got that interesting and particularly verbose exception when doing some XAML refactoring for a Windows Phone 7 application :

An unhandled exception of type 'System.Exception' occurred in System.Windows.dll
Additional information: 0xc00cee65

Turns out it was due to this :

 

xmlns:ucontrols2="clr-namespace:Company.Views.Controls;assembly=Company.Views.Phone"  
xmlns:ucontrols="clr-namespace:Company.Views.Controls;assembly=Company.Views.Phone"

 

Where two xml namespaces were referencing the same CLR namespaces and assembly. Merging the two namespaces fixed this issue.

 

Tough one...