i have fixed the problem.
i have put one HiddenField variable at my usercontrol page:
<asp:hiddenfield id="hid_choosingField" value="" runat="server" xmlns:asp="#unknown" />
then i have accessed and changed it from aspx.cs page:
Control hidField = WebUserControl31.FindControl("hid_choosingField");
HiddenField ucHidField = (HiddenField)hidField;
ucHidField.Value = "1";
then i have put a if condition at the ascx page to check what is the HiddenField value and base on the value i show the related fieldset:
<% if (hid_choosingField.Value == "1")
{
%>
<fieldset id="uc3Fieldset1" style=" height:350px;">
<legend>New Module Details</legend>
<asp:label id="Label2" runat="server" forecolor="blue" text="This is User Control 3 Panel 1 Fieldset 1" />
</fieldset>
}
else if (hid_choosingField.Value == "2")
{
<fieldset style=" height:350px;">
<legend>New Module Details</legend>
<asp:label id="Label1" runat="server" forecolor="blue" text="This is User Control 3 Panel 1 Fieldset 2" />
</fieldset>
i hope it would be helpful. thanks