checkbox selection from checkbox list

Hi All,
I have one checkboxlist ,in that two listitems are there.
<asp:CheckBoxList ID="chkFilerIndicate" TabIndex="1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="chkFilerIndicate_SelectedIndexChanged">
<asp:ListItem Text="Payment settlement entity (PSE)" Value="1"></asp:ListItem>
<asp:ListItem Text="Electronic Payment Facilitator (EPF)/Other third party" Value="2"></asp:ListItem>
</asp:CheckBoxList>
Here user can select only one checkbox , if user select another checkbox , previously checked checkbox should unchecked .
How can i achieve this?
and also without checking any one checkbox user cannot save their details
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