I'm having the same issue, the problem started last Tuesday after maintainace and the only premades I've been able to waitlist for have been those from my server. I believe the issue is on Blizzard's end, something to do with b.net requests not being delivered. Seems there's nothing that can be done on our end :(
This thread has a bit more info.

http://solidice.com/forums/1/topic/cant-create-oqueue-group

Can't join any waitlists in Oqueue

Hey folks. Big fan of Oqueue, but sadly I'm having some issues. I simply can't add myself to any waitlists.. I click the 'Join Waitlist' button and absolutely nothing happens. No declined-sound, no change to 'Pending'. :( I have the most recent version and have uninstalled/reinstalled the addon, nothing's worked. Thanks in advance for your help.