Yes, thanks for the tip, I have removed it. However, it has been my login for years with no problem, but the instant the problem occurred I was banned. When I put the url in my browser something adds '?nologin' to it, and this 'something' can only be Avast.
Summary: while I was downloading a 3gb .zip file with no hidden virus, Avast suddenly blocked everything in sight including forum access. There were no warnings, explanations, or clues in the UI. When I finally stumbled on the 'cure', the browser was able to complete the download uninterrupted. 1984 comes to mind.
Incidentally, I am asked for my email address when I click 'login', not my user name which appears to be the name part only of my address.