False DTD Entity errors

I am encoding urls into javascript variables and then executing it using
window.location.

 

The W3C validator is returning errors saying that the general entity is not
defined

 

I cannot give the URL of the page as it is password protected, however here
is the code that is being used.

 

var xMax = document.documentElement.clientWidth, yMax =
document.documentElement.clientHeight;

var xNew = (xMax - 210);

var yNew = (yMax - 230);

var url = "http://.../boundary_tool.php?x=" + xNew + "px&y=" + yNew + "px";

window.location = url;