This error was originally reported as an issue with Bible module on the Drupal.org web site by another user. I don't know if the original poster is still having the same problem, but I am getting the same error on my Church web site with the Bible module installed. I am running the latest version of Drupal 7 with version 7.x-1.4 of the Bible module.
Any time a progress bar is displayed (for example: when checking for module updates or running a bulk operation) , I initially see two progress bars at the top of the page. As the progress bars start to update, the first (probably erroneous) progress bar disappears and then I get the following error message:
An AJAX HTTP error occurred.
HTTP Result Code: 404 Debugging information follows.
StatusText: Not Found
ResponseText: Page not found | Church of the Master United Methodist (rest of error deleted for space).
If I scroll down past the error box, the second progress bar appears to be operating normally.
I have confirmed that this error is originating with the Bible module since when I disable that module in the admin pages, I do not get the error.