I use to get this error too, but i was using eclipse juno not j2ee, i just had to reinstall eclipse worked for me. Hope it works for you too.

Hi, the way i understand; you have a computer somewhere that is not connected to the internet, then you want something to just give you all the packages for you to download then install them on the machine with no internet connection. Well maybe not like Ubuntu Software center online look alike but their is this software