I'm trying to run a Sage notebook server in a screen session (though I don't think the specific program is relevant because I've seen similar behavior for other programs). While I'm logged in to the machine (via ssh), it behaves as expected, regardless of whether its screen session is attached. After I've logged out (leaving the program running in the detached screen session), the server continues to run, but begins to have errors that seem related to not being able to see/access certain files. If I ssh back in (without touching the detached screen session), the errors go away.
This is a pretty vanilla Ubuntu Server 14.04 (32-bit) install. What's different between being logged in and being logged out that could cause this?
(This relates to my SO question here.)