On most different types of systems that I login using, I get a message that looks some thing like this, right after I enter my username and password:
Then, no matter what I do, it won't let me log in, unless I click in the FireFox or Internet Explorer address bar and hit <enter>. Then, the page fully loads and everything is OK. Sometimes I even try to enter in my username and password twice, and it still doesn't fully login, but it does seem to partially log in. So I think there's some kind of a bug in the login script. It didn't used to happen back in early 2013.
If you fix this, I think you'll get less complaints from people having trouble logging in and possibly even more users if people had given up in the past.
I get the problem in Mozilla FireFox, Internet Explorer, but I think I didn't get it in QupZilla but I did get it in Chrome I think or maybe visa versa. I get the problem on WIndows, Linux, and MacOS X.
This is still the best forum on the internet.