WriteableBitmap protected .pixels

Question

Hello,
I have a silverlight application which is hosted within a WCF for purposes of getting at the data access layer.  I am trying to convert a UI element on the silverlight side to an image using WriteableBitmap.  However when ever I hit .pixels I get a protected error.  Most of my research is telling me that this is a cross domain issue, but the WCF is hosted within the WCF and shouldn't that mean they are on the same domain.  Any help here would be appreciated.
Thanks,
Derek