what does "FM" mean?
It happened before, to you this time, it probably will happen again, to you or somebody else. If we do not find out what happened this time, we will be exactly where you were on your first post when it happen again.
I do not know how rsync works. It connects to the server on port 873? I think normal access to the repositories is on port 80. Maybe this is why others manage to connect correctly? They were using synaptic and it was connection on port 80 and your were failing because you were connecting on port 873?