Why can't I invite more people to my alliance ??

I have 9 members in my alliance. For some reason I cant invite any one else to my alliance or people who tried to join get the message that reads.

"Maximum unique player player count has been reached."

I also get this message when I try to invite someone.

The other issue I seem to be having is that some of my members can not join the closed alliance match I have started.

That message reads.

" You cannot select a different player from the alliance league any more. Maximum unique player count has been reached. "

Can any one tell me what is going on? I thought you were able to have a maximum number of 20 members in an alliance and why cant some of my members join my closed alliance match ?

Thank you

Alpha_Zulu