>...only now it's not limited to weekends. It just happens, usually on both UT and Chatter, not necessarily at the same time. The script which refreshes the top bar never finishes.
>Most of the times there's a message mentioning "unexpected" or something like that. Then I have to log in again, to both forums separately. Don't know how long they are unavailable each time, I just close both tabs and check them later, and that's usually later enough that they are accessible again.
>
>Before this began, I stayed logged in for weeks. I guess technical progress has its victims.

Just speculating but maybe Michel has these sites on a virtual server, and that server is on a plan which shuts it down after a period of inactivity. Then, when a new request comes in the server restarts but is not immediately available. If you find you're able to log on a couple of minutes after getting a 404 that might be what's happening.