Created 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?