I've been having similar issues. It is a real hit and miss deal at the moment. I was on earlier and downloaded one file before they came back with the infamous phrase: "we're awful busy at the moment. Please try later."
Now I can't get in at all.
The odd thing is that of late, Avsim is having all the sign-on problems, whereas Flightsim now is completely accessible. I can't remember the last time I got an "All nodes busy" response. Go figure