Question: Whats the best way to have file attachments in blocks like you can with nodes? Is this possible with an existing module?

Answer: 
Same problem that you and it was driving me crazy.
My configuration is eclipse indigo over windows 7 and glassfish 3.1.1. The jdk I'm using is 1.7x64. I downloaded the glassfish server tools through the new server window.

I have solved it (it currently works, who knows what's happening in the near future) downloading and installing jdk1.6.30. I haven't uninstalled jdk1.7, but I've configured my eclipse project to use jdk1.6 instead.
Hi all I found solution for debugging problem. In my case Eclipse Indigo and linux x64 it works. More details in other thread about the same error <https://stackoverflow.com/a/14551690/1976844>