New known bug the Wiz 8 tech team is working on:
"If you have an all female party, with a male RPC traveling with you, Al-Sedexus won't let you offer up a female and the RPC can't be picked either. (Workaround -- dismiss the male RPC, then choose party member)"
If you have a male RPC with you, drop him and try again. If this option fails, it looks like you'll need to wait on the next patch.
