PageMethods Returning "Authentication failed" Errors

Hi!
In an ASPX page, I have the following code:
  
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true" />
<script language="javascript" type="text/javascript">
function OnSucceeded(result, userContext, methodName)
{
alert("It's good: " + result);
}

function OnFailed(error, userContext, methodName)
{
alert("Error: " + error);
}

function GetPassword(e)
{
var email_control = $get('<%= ...