I am trying to automatically reRender a datatable when user click on Ok button on a modal panel. For whatever reason it isn't refreshing. What am I doing wrong here? Any help will be greatly appreciated.
I'm not surprised. Despite being on the same view definition, I'd expect the modal panel to pretty much behave like an independent view.
Since the modal panel blocks the background view (that is, after the definition of a modal dialog), you should expect that the background view is going to remain static.
The solution to that is probably going to be that you trigger the background reRender events as part of the ModalPanel's dismissal operation. Roughly speaking, that means an "onclose rerender" operation.
Sometimes the only way things ever got fixed is because people became uncomfortable.