Using PageMethod inside CustomValidator

Hi,

I'm trying to call a page method inside CustomValidator client function with ASP.NET AJAX:

function ValidateAccount(source, arguments)
{
   ...........
   ...........
   ...........

   PageMethods.IsAccountExist(accountName, OnSucceeded, OnFailed);
}

function OnSucceeded(result, userContext, methodName)
{
   if (result == false)
      //do not make a postback
}

How can I prevent a postback in OnSucceeded function? I set CustomValidator.IsValid to false, but a postback still occurs.

Thanks for help,
Ayelet.

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