i did some searching in this case and here are the facts:
-problem only occurs with comodo firewall
-problem is the java webstart splash screen function
-problem can persist, even if you disable the firewall
solution:
the most effective solution is to prevent the the java splash screen from starting up at all, when you start the client!
for xp you can edit the filetype options. in win7 you have to edit the registry for that.
the crucial point is to add "-Xnosplas" after ..\javaws.exe" startup line.
optionally you can add javaws.exe to the "trusted application" in comodo fw, but it does not help for some users as well. (like me on this pc :-/ , helped on my notebook though)