After successfully upgrading my cloud service to the new \"Azure SDK for .NET 2.5.1\" I got the following error when trying packaging/publishing.
I searched locally for the required dll and found it in almost all previous versions of the Azure .Net SDK had it (from v2.0 onwards I believe).
So in order to fix this you need to copy the following dlls from the previous version v2.4 of the SDK to the similar location for v2.5.
SDK installation paths.
Dlls to copy (missing):
Since there may be a better answer to this I will not mark this as an answer yet.