Thanks a lot Damyon, it works!
For those who get the same problem, some information (I'm not an expert but it could help):
- As Damyon said, the problem is the lenght of the URL (number of characters). The Php Suhosin patch has a defaut limit of 512 characters for get parameters. In my case, the URL had more than 900...
- To fix the problem, you have to change the suhosin.get.max_value_length = <limit> in the php.ini, for example suhosin.get.max_value_length = 2000
- In my case, I was not able to change it by myself (I changed the php.ini in Cpanel but nothing happens), I had to ask the web hosting team to do it for me (check with your web hosting service).
Thanks Damyon and Adam for your precious help.