I am facing the identical issue, using Acrobat Reader. I have the latest version, there are no updates available. It used to work perfectly fine, but recently I go through all the steps that kevinb has mentioned, and there is no movement upon clicking on the 'sign' button. It's been 3 years since kevinb posted this issue, one would imagine there is a solution by now.
Unchecking the 'use modern interface' option throws up the following error - pkcs#11 error code 0x100
I am using a Mac. Please let me know how to solve for this.