Well we went from this issue the other day
http://www.splashdamage.com/index.php?name=pnPHPbb2&file=viewtopic&t=12970
To now at least the connections go through and people can join, but the vast majority of them are getting kicked via PB for the PB INIT FAILURE crap. 
We havent changed anything on our servers and have had them running on our own dedicated box out of the planet for over a year now, with no issues.
Tried for the hell of it, do complete fresh install of ET and PB and doing a manual update on PB, still kicking peeps.
Anyone got any ideas?
Thanks