I had a lot of trouble getting my CustomValidator events to fire on a radiobuttonlist until I figured out that they needed to have ValidateEmptyText="true" in order to be invoked when nothing was selected.
Here's my complete CustomValidator:
<asp:CustomValidator ID="custvalBirthCenters" runat="server" ControlToValidate="rbBirthCenters"
ErrorMessage="Please indicate whether you attend births at birth centers."
Display="Dynamic" Text="*" CssClass="validation" Enabled="true" ValidateEmptyText="true" ></asp:CustomValidator>
Other things to check if it isn't firing:
- Does the ValidationGroup value match in all 3 places: the submit button, the validator control, and the control to validate?
- Does the submit button have CausesValidation=true