April 21st, 2015, 4:40 pm
There is currently a SA-MP exploit which allows anyone to flood any server with fake players that causes "normal" players to see that the server is full.
Just wait at the "Server is full. Retrying.." screen until you get connected, even if it may take a while.
Unfortunately there is no working fix for this exploit, so there is nothing I can do about it. All we can do is wait.