Webclient Message box not working

Hi,

when i try to implement message box in Webclient, it's not working same code is working in Desktop application.

Code :

namespace DotNetCustomization
{
[SupportedDexPlatforms(DexPlatforms.DesktopClient | DexPlatforms.WebClient)]
public class GPAddIn : IDexterityAddIn
{
public static IvItemMaintenanceForm ItemMaintenanceForm = Dynamics.Forms.IvItemMaintenance;
private IvItemMaintenanceForm.IvItemMaintenanceWindow
ItemMaintenanceWindow = ItemMaintenanceForm.IvItemMaintenance;


public void Initialize()
{
ItemMaintenanceForm.OpenAfterOriginal += new EventHandler(ItemMaintenaceForm_OpenAfterOriginal);
}

private void ItemMaintenaceForm_OpenAfterOriginal(object sender, EventArgs e)
{
Int16 answer;
answer = Dynamics.Forms.SyVisualStudioHelper.Functions.DexAsk.Invoke("RS test - please ignore", "Yes", "No", "Cancel");
this.ItemMaintenanceWindow.ItemDescription.Value = "RS Test";
}
}
}