Why am I getting an 'AllowCustomPaging must be true and VirtualItemCount must be set for a DataGrid

Why am I getting an 'AllowCustomPaging must be true and VirtualItemCount must be set for a DataGrid with ID MyDataGrid when AllowPaging is set to true and the selected datasource does not implement ICollection' Error?

You are probably trying to implement paging in a DataGrid while binding the DataGrid with a DataReader. To fix this, instead of using a DataReader use a DataSet