As you have mentioned that you are using the Telerik Controls.
You can use "RadAjaxManager1" to prevent your postback .
In your page load you can use the below code.
ScriptManager _scriptMan = ScriptManager.GetCurrent(this);
_scriptMan.AsyncPostBackTimeout = 36000;
RadAjaxManager1.AjaxSettings.AddAjaxSetting(Combobox1, Combobox2);
RadAjaxManager1.AjaxSettings.AddAjaxSetting(RadGrid1, RadGrid1);
RadAjaxManager1.AjaxSettings.AddAjaxSetting(btnSearch, RadGrid1);
RadAjaxManager1.AjaxSettings.AddAjaxSetting(cmdPlant, cmdCarCd);
RadAjaxManager1.AjaxSettings.AddAjaxSetting(txtCustCD, cmdCarCd);
RadAjaxManager1.AjaxSettings.AddAjaxSetting(btnCustCD, cmdCarCd);
You can find more details from telerik Web site
http://www.telerik.com/help/aspnet-ajax/ajax-ajaxmanager.html[
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