WP7 App doesn't work when ran from Visual Studio but once deployed on Device it works

Question

I am working on Photo application.
In which a user can upload, view, and download pictures to and from the cloud.
For back-end I am using buddy API.
The problem I am facing is that once I choose a photo and try to upload it to the cloud it gives me 'Null reference exception' and this only happens when ran from Visual Studio (either to the device or emulator).
But once its deployed on my phone it uploads and behaves normally.
I don't know where to exactly put the blame and from where to start looking into this problem.

It fails on:

var photo = await album.AddPictureAsync(e.ChosenPhoto);

with the error:

A first chance exception of type 'System.NullReferenceException' occurred in PhotoApplication.DLL