Working fine on localhost, not on server. PHP AJAX

>>> We have programmed a web application, for ordering food.

You're my hero!  

Are you in Linux or Windows?  Have you seen anything interesting in your PHP error log or your web server's error log?  Does the site not come up at all, or are you getting HTTP error messages?

One of the security features that browsers implement is that the HTTP Request calls cannot be sent to a different server than the original page was served from. For example, if your page is served at "http://www.mymaindomain.com", you cannot initiate HTTP Requests to "http://www.myotherdomain.net". This is fairly straightforward, and you should be able to determine fairly easily if this is the case.

A part that is a little trickier, however, is if your page is served from 'www.mymaindomain.com', but your HTTP Request are directed to 'mymaindomain.com'. The browser considers this to be a different domain, and will block the request.

If neither of the above are the cause of the issue, use Firefox and take a look at the Javascript console (on the Tools menu). This will contain helpful debugging information if your script is generating errors.

My localhost is on windows Apache, but think to is running Linux also Apache.
The site is displaying but it is not retrieving the HTTP requests. Can it by that the server is running different version of PHP.
My URL are relative so it should not call a different server.

Here is a section of my AJAX,js

function GetFromServer(xmlRequest, targetID)
{
      url = "Control/Control_Interface.php";
      startWait(targetID)
      //alert("THE FOLLOWING REQUEST WILL NOW BE SENT TO THE SERVER:\n\n" + xmlRequest)
      var xmlHttp = new GetXmlHttpObject()
      if (xmlHttp==null)
        {
        alert ("Browser does not support HTTP Request")
        return
        }
      xmlHttp.open("POST",url,true)
      xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded")
      xmlHttp.setRequestHeader("Content-length", xmlRequest.length)
      xmlHttp.setRequestHeader("Connection", "close")
      xmlHttp.send("xml="+xmlRequest)      
      
      xmlHttp.onreadystatechange=function()
      {
            if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
                         {
                              //alert("THE SERVER RETURNED THE FOLLOWING RESPONSE:\n\n"+xmlHttp.responseText)
                              ParseResponse(xmlHttp.responseText)
                         }             
      }

Thanks will check it out, we also found out that the server is running PHP 4, and we programmed in PHP 5. So think the problem is there as well.