Cant play solo/duo que with a friend, both unranked

Me and my friend finished at plat 1 and diamond 5 last season and now this new season when we are trying to play duo que we get this message

''You cannot join this lobby. The difference in rank between you and one or more players in it is too high.''

How come this happends and do we really have to play 10 games alone to play togheter again?