I just today I setup our new dkp website, ranks, rosters, etc...
When I tried to assign our Guild Leader (Bruhaa) a "Leader" rank, there's not a "Leader" option in the menu/pull-down. ("Leader" is the only rank missing from the menu.)
Also, when I use the "EQ2 Roster Upload" feature, the upload tries to synchronize him as "Leader", but it doesn't work when I hit 'Submit'.
This is because there can only be one Rank 1 on your site (Rank 1 is the top rank and owner/admin of the site), and "Leader" on your site happens to be Rank 1. What you could do, if you're not the Leader of your guild, is rename Rank 1 to "Administrator", and make a new Rank 2 called "Leader" (you can move it into place using "Move up" and "Move Down" as needed).