I've been having this problem for a couple of months now. To verify it I just created a new sg user, cleared all my cookies, cleared my Firefox cache and logged in to the secure https://www.spamgourmet.com. I was able to log in, but when I clicked the Advanced tab, I got a message saying "There was a problem with your login. Please log in again."
So I did that and after 3 logins I was able to get to the advanced page. When I clicked on the "Search Addresses" button I could see the list that contained the 1 sg address word I had created. When I clicked on the word to change the remaining number of messages to be forwarded, I again saw the "There was a problem with your login. Please log in again" message.
FYI I never check the "remember me" box, and I NEVER log in without going through the secure HTTPS connection. I also replicated this behavior using MS Internet Explorer so I do not think it is a Firefox-specific problem.
This is driving me crazy, and it happens all the time. I cannot log in long enough to do anything. Can anyone give me a clue as to what's going on or how I can fix this behavior?