I see... I think it is because it comes from a plugin.
Try updating the file:
webassist/progress_bar/emailActivityDetails_Universal_Email_2_Progress
line 13 has:
var thepage = "../../webassist/progress_bar/emailActivityDetails_Universal_Email_2_Progress_xml.php?" + Math.random();
try updating it to:
var thepage = "/webassist/progress_bar/emailActivityDetails_Universal_Email_2_Progress_xml.php?" + Math.random();