It happens all the time with the browser version, reg for MTTs and SNGs and they dont open up. Its by far the worst of any site Ive ever played on as supposedly you need to regularly clear your computers cache and do some other regular maintenance just for Sky Poker to work. The default line by Sky is to say "Well nobody else had problems so it must have been a fault on your end". However the downloadable software is much much better and Ive never had a problem with it so Id recommend everyone playing on Sky to download the client instead of playing in browser
if anyone has recently upgraded to firefox 4.0 there are issues at the moment with it and this could be one of the problems. If you are one of those could I suggest un-installing it and then going back to version 3.6
hope this helps