Which error is this?

[LadyForCamus]

I wasn’t exactly sure which sub forum to put this in. 

Which formal structural error is this? Is it still considered Affirming the Consequent if they’re using negations of p and q in the second premise?

The argument form

!p -> !q
q
------
p

is valid. In fact, !p->!q is logically equivalent (contrapositive) to q->p.  Then, with q, we can, in fact, conclude p.

The problem, as others have pointed out, is the assumption that !p->!q. This is what makes the argument unsound.

Thank you, Poly. I was so sure the structure was invalid I didn’t bother to check it against the valid ones! Hehe.