I was having the same problem. In fact, I still can not log in from the FFL page on byond.com. Instead use the byond pager to log in. It works for me everytime, it may work for you as well.
On the byond pager (you can open the pager by double clicking the byond icon beside your clock in the lower left corner) you should see a "Games" tab. Under that tab is a drop down menu. Select "RPG's". Final Fantasy Legacy will be in that list. Select it and it should turn blue. Click "Join" under the list of games and it will open up Final Fantasy Legacy.
I hope this helps those who can't log in.
~Hoob TheNoob