After upgrading from 6.3 to 6.5 and switching from NT to Linux my forum shows as "There are 0 registered and 0 anonymous users online." all the time...
It looks like you need to refresh the page at the same second that others to get any number there at all...
I noticed that in my admin part had a blank field "Who's Online Timeframe:" that i changed to 15 minutes.
Then everything seems to work more or less like before, does this all sound logic?