I was getting the error: The attachable property ‘Behaviors’ was not found in type ‘Interaction’.
This was generated by a missing reference to the "System.Windows.Interactivity" assembly.
You can download the assembly at http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=3062
It is contained in the BlendSLSDK_en.msi
You can extract the msi package without installing it, by using msiexec.
Just place the *.msi in C:\Temp and run:
msiexec /a C:\Temp\BlendSLSDK_en.msi TARGETDIR="C:\Temp\Blend" /qn