I have a 16 MB upload limit and yes I did experience the error before when trying to upload GroupJive. I had to delete all the groupjive installs and reinstall, but with with 1.8.1 upgrade install of community builder, I ran into the same problem as before as soon as I tried to install the main component.
There is a difference between IE and FF. Could you please try to register on the Firefox browser to our site, and then try to log into the site on an IE browser. you will see what I mean. I have tried logging in as an existing registered user on two different computers that I had never used before and got the same issue. Can access OK on firefox and access registered content fine, can log into IE with same userid and password and not be able to access content for registered users.