Sometimes just refreshing the page isn't good enough, you actually have to close the browser tab containing PF and open a new tab. Try this if you keep getting the "Site is down for maintenance" page. I'm sure it won't always work and is probably related to a redirect from the main page to the backup forum when the main site goes unresponsive.
This board is just generally f'ed up... ... it seems like every other month the place is down... ... for one problem or another... ... mebbe dey need to switch board software... ... and get a better brand.