Getting VERY strange AJAX/JS 404 errors
Ok well I seem to have "solved" the issue. 

I had a node with the following PHP code to take the user to their order page when accessing user/me/orders:

&lt;?php
  global $user;
  $orderpath = 'user/'.$user-&gt;uid.'/orders';
  drupal_goto($orderpath);
?&gt;


When I deleted that PHP code, everything started working again. 

Anyone know why the above code could cause the problems indicated in my question?