WPF DataGrid Scroll Event issue

I have a WPF program which incorporates the WPF customized DataGrid . The grid works fine in nearly all respects except scrolling. If I put the entire grid into a ScrollViewer, I can smoothly scroll through the entire grid, however, when i click the scrollbar,thenscrollbar is many, many, many times the height of the grid. Any and all suggestions are very welcome.