the reason that the ping would work is because it's using IP.. so it's going to use DNS... since there's no . after fileserver it's automatically going to append .domain.com (the origin)... (if you look in your options on your machine you're pinging from... in advanced you'll see the option to append this domain)... it's automatically filling it in for you. The reason it works with the full address is that it resolves without problem...
Thanks for clearing that part up for me, HTRegz.

I should stop doing any real work and commit myself to AO
Agreed.