i create dynamic checkboxes in coloum of table(<td id="trial" runat="server"></td>) from selecting quantity from dropdwonlist. well creating dynmic checkbox is not an issue.. well the issue is tht i am not able to check whether the Checkboxes is checked or not on a Button click.... the functiion used for generating dyamic checkbox.. protected void ddlList_SelectedIndexChanged(object sender, EventArgs e) { int no=convert.toint32(ddlist.selectedvalue); for(int i=1;i=<no;i++) { checkbox ch=new checkbox() ch.ID="chk_t"+i; ch.text="trl" trial.controls.add(ch); } } the function where i check whether checkboxes is checked protected void btnSave_Click(object sender, EventArgs e) { list<string> status_tn=new list<string>(); for (int j = 1; j <= no; j++) { trialid = "chk_t" + j; CheckBox checks=(CheckBox)trial.FindControl(trialid); if (checks.Checked) { status_tn.Add("Trial"); } } } in this function i get error : :System.NullReferenceException was unhandled by user code Message="Object reference not set to an instance of an object." Source="App_Web_pm_-zh7o" StackTrace: at btn_save_Click(Object sender, EventArgs e) in d:\Dot Net App\Talents\types_seeb.aspx.cs:line 325 at System.Web.UI.WebControls.Button.OnClick(EventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)