I have the same problem...have tried to run different versions, made sure the firewall is not interfereing etc.
strangely enough i used to be able to get on. Sometimes it would not let me on the directplay test host...i would retry and it would work, or not and i'd have to 'stir' things up a little in the software environment...
right now im gonna try to install v.534 ontop of a clean, fresh release version...
Id be interested to c what you figure out...ive been shut of the servers for months!