Clear it all: caches, history, web data, and anything that may be "holding" your browser information.
Turns out I had already created a login previously and I had forgotten about it. So this is resolved for me, but for future it would obviously better if an appropriate error message was displayed.
Yes! there is only one account on the forums here. What you can see depends on your "membership".
I think it's a lot more complicated than that. My problem is solved this is just a rant!:-)
The login for the FBA application didn't seem to work with the community login, so I did a password reset on the FBA application, and it gave me an opportunity to change the login, so I made it quarfie_fba thinking it was totally separate, so I could differentiate in my keychain, and I let the keychain set a password. So I'm into the application, and then I go back to the community and notice I've been logged out. So I try to login and it won't work, so I do a password reset on the community and I notice it has my new FBA application username, but the new password doesn't work, so I set a new password again with keychain. Now I go back to the FBA application to change the username back to quarfie and long story short I spent 15 minutes in a vortex trying to figure out what was going on, ultimately to realize that both services use the same account (username) but different passwords. Changing username changes everything, but changing password on FBA does not change the password for the community.
On the FBA password change page:
You may change your password to your FBA Company Information here. This password change below is ONLY to access your FBA Company Information, not the FileMaker Developer Community. To change your username and password in the FileMaker Developer Community, you must do it in “My Profile”.
So it warns you that the password is different, but it doesn't warn you that changing the username changes everything.
This sort of funny business gets really confusing with Keychain generated passwords because when you change them you overwrite the old one and there's no way to remember what it was, and then when you're trying to manage two different passwords on one web site, it obviously helps if the username is different, but at least the domain is different in this case.