I am not saying this is the only reason, but I believe part of this may be linked to one of the things they are doing to temporarily reduce congestion.

I've tested this several times now and I seem to be able to force this error. When I first log in, I can see the worlds. However, when I try to log in to Excalibur (my Legacy Server), I get the "World full Error".

Last night, I sat and basically spammed it until I got in (which is bad, I know and probably contributes to the connection congestion). However, This morning, after approximately 20 attempts to spam getting in, I would suddenly loose ability to see the servers.

This happens for EXACTLY 10 minutes each time; at which point it goes back to showing me the servers but telling me it's full (Have to Restart the Client). I have so far tried this 5 times in a row.

I just thought I would let other people know.

Good Luck!