“unrecognized selector sent to class” when calling category method from a library

Question

Problem

This question may seem a bit long, but I try to give as much information as possible, since I am really staggered by this.

I am currently working an a

Answer 1

Even though the answer is already selected, I wish the solution to my issue was here, as simple as it may be. Be sure to check that your class is properly checked in the Target Membership field under the File Inspector pane. If you fail to do so then it's only natural to receive the unrecognized selector sent to class error.