This is the error we get:
Error 1 The type \'System.Windows.Point\' is defined in an assembly that is not referenced. You must add a reference to as
We found it we had to go into the Silverlight folder and found the System.Windows.dll and now all is good thanks for the help though!
You'll also run into this error if you use the Portable Library Tools as it's not supported.
Add the assembly reference as you'd add any other framework assembly reference: