Wt.js

diff --git src/web/skeleton/Wt.js src/web/skeleton/Wt.js
index 0841bcb..6245652 100644
--- src/web/skeleton/Wt.js
+++ src/web/skeleton/Wt.js
@@ -746,7 +746,7 @@ this.pageCoordinates = function(e) {
   var target = e.target || e.srcElement;

   // if this is an iframe, offset against the frame's position
-  if (target.ownerDocument != document)
+  if (target && (target.ownerDocument != document))
     for (var i=0; i < window.frames.length; i++) {
       if (target.ownerDocument == window.frames[i].document) {
    var rect = window.frames[i].frameElement.getBoundingClientRect();