Trusted users and moderator ranks can not manually input a ban. I've tried checking and unchecking all the privileges to see if that was the problem. However no matter what they can not input a ban of any length.
As a temporary fix, you could change the privileges of your Full Moderator rank to the ones of your Moderator rank, and turn your regular moderators to full moderators. That would work if you don't have both full moderators and lead moderators already that you don't want to change the privileges of.