Thanks Peter for helping me with this issue! It turns out the web site rejects passwords that have '#' followed by numbers, as part of a security screen. So the remedy was simply to go to the web site and change my password to something not containing '#'nnn. 

I just purchased and installed ComicBase 2020. Upon launch it brings up a login dialog that requires a User ID and password. I have an account on ComicBase/AtomicAvenue that I can login to using my email address/password, but when I try to login with my User ID, that password does not work. So I clicked on the Forgot Password link, it sent me an email with a link, I clicked the link to get to a reset password page (for the User ID), and it errors saying that my email address is already in use. In other words, it won't let me reset the password associated with the User ID because the User ID is linked to my email address which has it's own account. Unfortunately, ComicBase 2020 will not let me login with my email/password account (which has all my product registration info) because it requires a User ID. So the product refuses to launch and I am dead in the water.