We tried various versions:
- Lesson from demosystem: Created, stored and restored on the same system. Didn't work.
- Lesson from demosystem to live system: Created, stored on demo, restored on live. Didn't work.
Demo and live system had the same versions, i.e. 2.3.1, 20120809.
The problem started off with one of our lecturers who created his lessons on a public test server whose moodle version is a later version than ours (our 2.3.1, 20120809 to 2.3.1, 20120907 or now even 2.3.2). You get a warning that there may occur problems in this last case due to missing backwards compatability which is quite understandable. But it should at least work with the other two cases, especially if you stay on the same server.
The filesize is 515KB but I also tried to use a smaller lesson with 66KB. No students data included. Only text, mimetex formulas, images are being used.
I'll try to create a lesson on the live system on Monday, store and restore that one on the live system. That's the only case missing.
Meanwhile any hints on what could cause the problems is welcome. If you need more information, please ask.