The Silverlight bits of DevForce 4.3.0.1 were built against the "standard" Silverlight 2 tools released in October 2008. It looks like Microsoft did not make the old assemblies and the December DataGrid release version compatible. DevForce is compiled against:
System.Windows.Controls.Data, Version=2.0.5.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
While the assembly in the December release is named:
System.Windows.Controls.Data, Version=2.0.5.0, Culture=neutral, PublicKeyToken=3d8c6023c75a3242
So, the assemblies were signed differently and the names don't match.
I don't know a workaround for this. I doubt that assembly binding redirection works in SL, and I don't know a way to add multiple parts with the same short name to the SL assembly manifest. We will research this further to see if we can address this problem, but for now DevForce 4.3.0.1 works only with the October SL 2 bits. (For the record, DevForce Silverlight 5.0.0.x uses Silverlight 3 Beta 1.)