do you use fasterfox?
is there anything else you did before that that may have set it off?
Do you usually stay logged in, or tell it to keep you logged in for 60 minutes? If you don't use fasterfox, here is what probably happened:
1) you logged in earlier in the day
2) you told it to keep you logged in for 60 (or however many) minutes
3) you went back to the forums 60 minutes and 15 seconds later
4) you tried logging in again, before 60 minutes and 30 seconds had passed
In other words, it automatically expired your session (logged you out) less than 30 seconds before you tried logging in, and the forums keep you from rapidly logging in and out (must wait at least 30 seconds between logging out and back in)
