Cannot invite friends to clan

[tocophonic]

Also posted this in the "Clans" sub-board. I'm not sure if that was the right place, so I'm posting it here as well. @Mods: Please feel free to delete the post that's in the wrong sub-board.

Hi there,
when using the Clan Management site at http://clans.faforever.com to invite my friends into my clan (My Clan -> Invite Players), I can not find them in the list. I tried several player names - even names of random people who were online according to my FAF client at that time, neither did show up.

What can I do?

thanks in advance,
toco