I honestly can't figure out what it is. I tried various combination of disabling java/javascript in three browsers (opera, firefox, IE7), but in all cases I didn't get any error messages at all - just a blank room.
It should be noted, by the way, that Java doesn't seem to be a requirement for the Buzzen webchat (only javascript and flash).
I then uninstalled flashplayer, and naturally the chat did not work without it - but no error messages either (apart from those of firefox about missing plug-ins). I let firefox install the flash player plug-in and upon refreshing, the chat again worked fine.
I then proceeded checking their forums, and I noticed a couple of other threads about connection problems - problems that might be related to the latest version of flashplayer, but then you wonder why re-installing flash didn't break it for me.
Again - I'm stumped, I don't know what could cause your problems. You'd think that if the flash player plug-in was somehow corrupted, re-installing it would do the trick (which you said didn't).
I think your best bet is still their helpdesk since they are likely to be more familiar with their product than I am, and they may have had to deal with similar cases before.