Hello,

Just sharing the solutions from the duplicate support thread, for better visibility from the community:

Here is one approach you can take to validate a RadCheckBoxList inside a RadWizard:

1.  Enable Unobtrusive Validation for your application.  We have a dedicated tutorial which goes into more detail on how to do this. For .NET 4.5+, the client-side validation requires just setting the following key in the web.config:

• http://stackoverflow.com/questions/16660900/webforms-unobtrusivevalidationmode-requires-a-scriptresourcemapping-for-jquery

• <configuration>
    <appSettings>
      <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />

2.  Use a CustomValidator instead of a RequiredFieldValidator.  Using the clientValidationFunction will allow you to determine if a checkbox has been selected using client-side code.  

<telerik:RadCodeBlock ID="RadCodeBlock1" runat="server">
    <script type="text/javascript">
        function RadCheckBoxValidation(sender, e) {
            var checkboxlist = $find(sender.controltovalidate);
            var selectedList = checkboxlist.get_selectedItems();
            if (selectedList.length > 0) {
                e.IsValid = true;
            } else {
                e.IsValid = false;
            }
        }
    </script>
</telerik:RadCodeBlock>

3.  Set the same ValidationGroup for the RadWizardStep, RadCheckBoxList, and CustomValidator. 

4.   Add the RadCheckBoxList as the CustomValidator's ControlToValidate.

<asp:CustomValidator ID="customValidator1" runat="server" ValidationGroup="validationGroup1"
    ControlToValidate="Questionnaire" ForeColor="Red" CssClass="questionnaire-validation-message"
    ErrorMessage="Please choose at least one of the options displayed" EnableClientScript="true"
    ClientValidationFunction="RadCheckBoxValidation" />

5.  The RadWizardStep needs to have its CauseValidation property set to true.

<telerik:RadWizardStep StepType="Step" CausesValidation="true" ValidationGroup="validationGroup1">
   ...
</telerik:RadWizardStep>

For more details on validation with the RadWizard, please take a look at this documentation.

Regards,
Peter Milchev
Progress Telerik