Dear Michael,
Did you manage to figure this problem?
"Both return a 500 server error in the browser: The website encountered an error while retrieving http://moo.priestley.ac.uk/course/editsection.php. It may be down for maintenance or configured incorrectly. "
We experienced exactly the same thing when we tried to activate the Plagiarism plugin on our production site:
https://moodle.org/plugins/plagiarism_turnitin
Version : 20150406, Moodle 2.8.6+, 3 clusters.
The plugin works on our test site without problems, and also the "normal" Turnitin Two" assignment is all right on both the production and test sites.
But after we activated this on the production site, the error messages started to pop up from time to time, and after we disabled the plugin they stopped immediately. What we found is that the file system on our production site had some problems and sent error messages like:
PHP Warning: mkdir(): No such file or directory in ............................moodle-2.8.6+/lib/setuplib.php
Now we repaired the file system, and will give an other try to the plugin when the classes are not that busy.
Best regards,
Gabor