I get a strange problem quite often that only affects two sites - both forums (one is this one, the other is avforums.com). I'll be browsing away quite happily, then all of a sudden PF won't work (I get the above message) and avforums.com just sits there trying to load, but only showing the background and nothing else, still trying to load, but never does.

The only way out of it is to open Network Connections, disable my LAN port, then unplug the power from the modem, leave it a few seconds, plug back in, let it start up, then re-enable my LAN connection on the PC. Sometimes this doesn't work and I have to do all the above again, then it works...

It's fucking annoying, but only ever seems to affect two forums I use - everything else works perfectly!