This does not work when there are validator controls on the page. To fix this, add the following lines to the start of the javascript function (before the line 'oButton.disabled = true;'):

if (typeof(Page_ClientValidate) == 'function')
if (Page_ClientValidate() == false)
return false;

Also, I have found intermittent problems with the button's server-side click event handler firing twice (it seems to happen on our production server where the postback round-trip takes longer than on my dev PC). To fix this, add a "return" to the end of the button's OnClientClick property:

btnSubmit.OnClientClick = "disableButtonOnClick(this, 'Please wait...', 'disabled_button'); ";
btnSubmit.OnClientClick += ClientScript.GetPostBackEventReference(optionsSubmit);
btnSubmit.OnclientClick += "; return;";

Hope this helps someone

Andy