RadAjax controls fully support server and client-side validation.    
    
    This example demonstrates how to achieve the desired functionality in a straightforward          and simple way with the RadAjaxPanel control. You can also use the          RadAjaxManager for the same purpose. In order to use the server-side validation,           you must add the panels with the validator controls in the UpdatedControls                 collection for the Register button:
        
        
        C# code:     
    
        
            
                private
                void
                RegisterButton_Click(
                object
                sender, System.EventArgs e)
            
        
        
            
                {
            
        
        
            
                    
                
                    ...
                
            
        
        
            
                    
                
                    if
                    (RadioButtonList1.SelectedIndex == 1) 
                    // Update the panels with validators only if server-side validation is performed.
                
            
        
        
            
                    
                
                    {
                
            
        
        
            
                    
                
                    // RadAjaxManager1.AjaxSettings[0] specifies the settings for Ajax requests initiated by the Register Button control
                
            
        
        
            
                    
                
                    AjaxUpdatedControl updatedControl1 = 
                    new
                    AjaxUpdatedControl();
                
            
        
        
            
                    
                
                    updatedControl1.ControlID = Panel1.ClientID;
                
            
        
        
            
                    
                
                    RadAjaxManager1.AjaxSettings[0].UpdatedControls.Add(updatedControl1);
                
            
        
        
            
                    
                
                    AjaxUpdatedControl updatedControl2 = 
                    new
                    AjaxUpdatedControl();
                
            
        
        
            
                    
                
                    updatedControl2.ControlID = Panel2.ClientID;
                
            
        
        
            
                    
                
                    RadAjaxManager1.AjaxSettings[0].UpdatedControls.Add(updatedControl2); AjaxUpdatedControl updatedControl3 = 
                    new
                    AjaxUpdatedControl();
                
            
        
        
            
                    
                
                    updatedControl3.ControlID = Panel3.ClientID;
                
            
        
        
            
                    
                
                    RadAjaxManager1.AjaxSettings[0].UpdatedControls.Add(updatedControl3);
                
            
        
        
            
                    
                
                    }
                
            
        
        
            
                }
            
        
     
    VB.NET code:  
    
        PrivateSubRegisterButton_Click(sender AsObject, e AsSystem.EventArgs) HandlesRegisterButton.Click
            ...
                IfRadioButtonList1.SelectedIndex = 1 Then' Update the panels with validators only if server-side validation is performed.
                    ' RadAjaxManager1.AjaxSettings(0) specifies the settings for Ajax requests initiated by the Register Button control
                    DimupdatedControl1 AsNewAjaxUpdatedControl()
                    updatedControl1.ControlID = Panel1.ClientID
                    RadAjaxManager1.AjaxSettings(0).UpdatedControls.Add()
            (updatedControl1)
                    DimupdatedControl2 AsNewAjaxUpdatedControl()
                    updatedControl2.ControlID = Panel2.ClientID
                    RadAjaxManager1.AjaxSettings(0).UpdatedControls.Add()
            (updatedControl2)
                    DimupdatedControl3 AsNewAjaxUpdatedControl()
                    updatedControl3.ControlID = Panel3.ClientID
                    RadAjaxManager1.AjaxSettings(0).UpdatedControls.Add()
            (updatedControl3)
                EndIf
            EndSub