similar issue to poorcomputerman in january 2018
I've tried MOS, MOS Technology, Commodore Business Group, 6502, 6510 and variants.
I cannot answer this question to complete registration.
EDIT: the registration page is not intuitive to provide enough feedback to say you have entered the answer for the security question.. it was only because a notification said to activate my account that I was able to eventually muddle through to access.
just giving feedback.