I know that people use proxy servers to avoid bans but this is not my case. I use it to be able to connect CH, i'm not banned.
Well, thanks anyway for your interest.
I can only find an explication:
Earlier today i got 404 error. Then i changed public ip (range 79.*.*.*) to avoid ratio control in a tracker (sorry but my upload is very bad ) and with the new ip i can access to CH (range 83.*.*.*). It must be a ip range banned by admins in CH or some problem with that ip range. I know other people with Telefonica as internet service provider have the same problem as me with CH.