I'm new to Drupal, and I'm working with a Drupal site that someone else wrote. From the admin menu, when I go to Structure -> Pages -> Edit Content -> Gear Menu -> Edit (or Settings), Drupal throws up this error:
"An AJAX HTTP error occurred. HTTP Result Code: 200 Debugging information follows. Path: /panels/ajax/editor/edit-pane/panel_context%3Apage-join_step_two%3Apage_join_step_two_panel_context/4 [...] RESPONSE = nullnullnullnullnullnullnullnullfalseCancelled: Error bad character content for element 'data_key'________nullnullnullfalsenullnull"
The code is also inserting the line
"RESPONSE = nullnullnullnullnullnullnullnullfalseCancelled: Error bad character content for element 'data_key' ________ nullnullnullfalsenullnull"
at the bottom of every page.
I know that Firebug can cause the Ajax HTTP 200 error, but I don't have it installed. I've spent hours looking through help pages for this error, and nothing has worked. Can you help? Thanks!