i have problems too. In wp7 it always worked fine (in 12 apps), but i can't get it running under wp7.1. First i had problems with System.Windows.Interactivity, it was an older version than mine. Now with the update i get following error:
System.ComponentModel.Composition.ChangeRejectedException was unhandled Message=The composition remains unchanged.
The error even occurs in a empty project with just msaf. It crashes on :
==> <mwa:WebAnalyticsService />
I tried with version 1.5.1 and 1.5.3 and the last wp7 sdk.
Help is appreciated.