SmartAssembly isn't able to embed this assembly because it's signed with Microsoft's strong-naming key. However, a possible workaround is signing the assembly with a different strong name key:
1. Open a Visual Studio command prompt
2. Navigate to the directory where the dll is located
3. Type "ildasm System.Windows.Interactivity.dl" --this will open the dll in Ildasm
4. In Ildasm, go to File>Dump and click "OK" -- then enter "System.Windows.Interactivity.dll" as the filename and choose the location where you want to save the IL file
5. Go back to the VS command prompt and if necessary, navigate to the IL file's location
6. Type "ilasm System.Windows.Interactivity.il /dll /key:YourSNK.snk"
(where YourSNK.snk is the strong name key you'd like to use on the dll)
7. The dll will then be created with the new SNK and you should then be able to merge/embed the assembly
Hope this helps!
Red Gate Software Ltd.