Hello,
Thank you both for your replies ! We use Moodle 2.4, and I just checked and see that they disabled assignment 2.2 so we work with the new one.
As to the cron, you wouldn't believe it, but it's just about burocracy (they tell me they have to check that out, and are checking it out since about one year and a half - and I don't have a server access). But I don't give up, they'll put it one day.... I launch it once or twice a day manually.
But actually, I saw that on our test platform (that one is 2.5), the calendar does work (the date of an assignment I created was automatically added) - and I suppose that there's no cron for that platform either...
One other question : besides assignment due dates, are there any other dates that should appear on the calendar?
Thank you very much for your help !
Ulrike
PS: as to the environment, I'm going to ask, and come back when I get an answer