Commented Unassigned: The invocation of the constructor on type 'Xceed.Wpf.DataGrid.DataGridControl' that matches the specified binding constraints threw an exception. [20931]

I added the xceed.wfp.Datagrid assembly reference dll. After which i added the DataGrid in my XAML. when i try to run i get the following error.

Did any one run into this issue. I"m running .net framework 4 VS 2010. Could someone tell me what am i doing wrong?
Comments: ** Comment from web user: justin0805 **

I found the soulution. I was using runtime version v2.0.50727. I removed that reference and added a new reference that had runtime version v4.0.30319 and it worked.