var prm = Sys.WebForms.PageRequestManager.getInstance();
prm.add_initializeRequest(InitializeRequest);
prm.add_endRequest(EndRequest);

// Executed anytime an async postback occurs.
function InitializeRequest(sender, args) 
{
    $get('divLoadingAnime').className = 'divUpdatePanelProgess';
    $get('divSubmitBtn').style.visibility = "hidden";
}

// Executed when the async postback completes.
function EndRequest(sender, args) 
{
    $get('divLoadingAnime').className = 'divUpdatePanelNormal';
    $get('divSubmitBtn').style.visibility = "visible";
}