Urgent server side mulirowselection gets lost if the page is posted(Ajax) seveal times

[kachy]

I have a radgrid in a RadTabStrip which is enclosed in radAjaxPanel. For radGrid multirowselection is true and clientsetting row select is false. I am selecting the row server side with a checkbox checkedchanged event as explained in server side row selection demo. If I select 5-6 rows then all the selections are lost but the checkboxes are still checked. What can I do to fix the problem. If I select only 2-3 rows, all remain selected.
Please let me know some solution, its urgent.

Thanks