Thanks for the reply! Appreciate it.
When I edit a default setting for a module, say Quiz, I cannot alter the values of the fields. When I click "save changes", it does simply refresh the current page and nothing happens. The green message "changes saved" does not appear. So it basically does nothing at all.
When debugging is enabled, no new debug messages will be displayed. Only the same warning message all throughout the site is displayed which I think, has nothing to do with the problem.
Please see the video:
Switch to the Boost theme temporarily. Does it make any difference?
Still with Debugging on, check your web server's error log. Has anything found its way in there that might help?
I actually did that and it did not solve the problem.
Fortunately, I solved the problem by deleting the contents of the following folders in the moodledata:
cache, localcache, sessions, temp, trashdir
I should not have copied these folders when I migrated to the new server.
Thank you very much for your time Sir Howard Miller!