Got it. Those settings define who can VIEW a section. There is a different bunch of settings that define who can CREATE topics / CREATE posts. The moderators do not have access to that second set. Whoever created that section tried to restrict CREATE to "senior" members of the forum (an excellent choice in my opinion; an understandable mistake in my opinion).
The SMF programmers definitely need a lesson in communications.
Time for some fixin... Done.
@PaulS, thank you for reporting the trouble! Please let us know (use Report-to-moderator!) if you find anything else.