I am having a similar problem. I set up the subsonic software on my Windows PC and the App on my Android. As long as I am home I can connect to my wifi network and my music streams flawlessly. However, when I try to use the 3G network I get the same "Network error" message thta sk8russ is getting.
I can connect to the demo server fine, but when I try to connect to my own server I get the error. The server address I have in the phone is
http://(mylogin).subsonic.org
mylogin is the name I created when I set up the software on my pc.
With regard to the comment below about how some things might not work if you haven't donated, I'm not clear on that. I haven't donated yet because I wanted to make sure that the program was going to work for my needs first. If it does I certainly will donated. But I thought that was what the 30 day trial period was about.