Riot please explain this

,,YOU ARE NOT PREPARED!"

Try going through every que until it let's you click play. For me, going to coop then switching back fixed it.

Looks like you are not ready in the eyes of Rito :^)

Jokes aside, I also already encountered that bug, even better versions from time to time. Like when we were 5 premades and I couldn't switch from aram to normal draft because it said we are more than 5 people (what??) and one time we couldn't play ranked because one of our teammates wasn't level 30 yet.....in a normal draft group full of people over level 100....

Leaving the lobby and creating a new one fixes these bugs most of the time ^^