We have the same issue – but not for everyone. I can’t login on my Mac with Safari, but with Chrome I could after clearing the cache. Another member with admin privileges running Windows is unable to get in with IE or Firefox, but I know one of our paying members is able to login because I just got an email notification that she uploaded an event to the site. 1and1 said they’re working on it, and they gave me a “24 – 48 hour” time frame for resolution.
