I have www. on my URL and am not breaking the rule. The problem actually seemed to start after I "stopped" breaking the 2 dot rule. I started up v5 and did not have the www . I was informed to add it due to the 2 dot rule. Yesterday and early today I was not having the problem. I fixed the site to adhere to the 2 dot rule later today, added www. to the URL, and that's when I started noticing the username problem.
I don't think it's my connection- I have a good 2MB/1MB line. I have two lines, I'll try the other and see if the problem persists.
UPDATE: I have two t-1 speed lines. I switched to the other line and I don't have the problem. In other words, if I add a new product and do something else for a while, it does not prompt me for username/password like it was doing before. I guess it is related to the quality of the line. Th line giving me problems works well for everything else- I get 4MB down and 1MB up. I guess I need to have it checked out.