Can't read level II books despite level 6 reading

Can anybody tell me why, despite learning to read and levelling it up with primers to level 6, I still can’t read skill books that are level II and which in their info window say that they require level 5 to read?

You have to have that level of the book you’re learning. If the book is for lvl 5 lockpicking you need that in order to read it, not lvl 5 reading

Ah … I was wondering if that was the case but couldn’t immediately see a skill that matched the book. But maintenance seems to match a book about honing weapons. Cool. Thank you. =)