function detectUserName(userName, infoDiv){
    
    var xmlhttp = false;
    try 
    {
        xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
    }
     catch (e) 
     {
        try 
        {
            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        } 
        catch (E)
        {
            xmlhttp = false;
        }
    }
    
    if (!xmlhttp && typeof XMLHttpRequest!='undefined') 
    {
        xmlhttp = new XMLHttpRequest();
    }
    
    var username = userName.value;
    
    var url = "/PPsecure/checkuser.aspx?module=check&username=" + username;
    try
     {
        xmlhttp.open("GET", url, true);
    }
     catch (e) 
     {
        
    }
    
    xmlhttp.onreadystatechange=function() {
        if (xmlhttp.readyState==4) 
        {
            var status = xmlhttp.status;
			var ReturnValue = xmlhttp.responseText;	
		    ReturnValue=ReturnValue.substring(0,4);
            if (ReturnValue=="true")
             {
                globalObj = userName;
                userName.select(); 
               //alert("该帐号已经存在，请重新输入");      
                showInvlidormatErrorInfo(userName, 1);
                existedUser = true;
               return false; 
            }
            else
			{
                successInfoBox(userName);
                globalObj = null;
            }
        }
    }
    
    xmlhttp.send("");
}