The following code does not bind the RadDropDownList:

DataSet ds = oLkp.GetLookupValues("matterTypeId, matterType", "tblMatterTypes", "matterType");
this.cmbMatterType.DisplayMember = "Lookup.matterType";
this.cmbMatterType.ValueMember = "Lookup.matterType";
this.cmbMatterType.DataSource = ds;