Presumably, the files play okay if you play them over an NFS mount or move them locally? I'm no expert, but it looks to me like this is a communication error between the addon and the backend, but I guess you'd worked that out yourself. What I don't know is whether this is due to congestion on your LAN, some hiccough on the OE box or the backend, an I/O bottleneck (is your backend doing anything else when this happens?), etc. Could something be saturating your LAN connection on your server, are you running a backup, streaming HD files, or otherwise hammering the box, the hub it's connected to, the LAN segment...?
There was also a comment on the xbmc forums about a similar error message, and this was related to clock difference between the front end and back end (I think, the forum is down at the moment so I can't check).
Not necessarily much help to you, though...
