Because of the new forum update, some folks have been having issues. Whenever we have a big forum update like this, the best solution is to clear your browsers history and cookies.
Clear your browser, history and cookies.
for Firefox it is Tools >> Options >> Privacy >> Clear your Recent History (middle of popup) then click clear individual cookies and clear them all out.
I actually suggest that anyone that is having issues try this (including the log in issue) and then tell me if you are still having the problem.
Since not everyone is having the issue it usually means that it is a browser problem on your end.