A quick grep through the source doesn't make it immediately apparent where this table it being populated. We have a user who is trying to use the netgui (https://www.isi.deterlab.net/clientui.php3) to edit an experiment, but the xmlrpc server is trying to get the nsfiles from the table and they are not there.
Oops, the nsfiles table has been deprecated, which means that the xmlrpc server is doing the wrong thing. What version of Emulab are you running? Not sure what needs to change, but if you are running recent code, at least you can pick up the fix easily. Lbs