I'm at a loss here ... not sure where to look for this issue. Here's the setup and description of symptoms:

I have a server set up with video files on them (mostly .mkv). It's running Ubuntu 12.04, though that's a recent upgrade. Until last week, it was on Ubuntu 10.04 (things worked fine then, so obviously the upgrade changed something).

I have a second PC (Ubuntu 12.04, no recent changes) connected to my TV in another room. They're physically wired together through a router.

When I play a video back over the network, it will play fine for a period of time, then stop. Always at the same moment in each video, though that moment is different for each video. EG: One video is 392.8MB and stops at 7:28 / 1:29:21 minutes. Another is nearly the same size at 392.5MB and stops a 7:32 / 1:28:27. Yet another is 1.2GB and stops at about 11:04 / 2:06:50.

I'm trying to play through both XBMC and Totem. Neither throws any errors on the video stop, just transitions to the next screen. In XBMC that means going back to the menu as if the media were finished. In Totem, that means going on to the next video in the playlist.

Now, it /appears/ that the files are stopping at nearly the same /percentage/ of completion. Doesn't appear related to file size (to me). It also happens regardless of whether I skip forward or back in the video. I can jump to right before the stop and it'll still stop.

I tried copying the video over locally using sftp, which was fine (and I copied a large file to ensure I was connected longer than 10 minutes as another test). Both tests worked fine. I could copy large files with no connection drop, and once the file was local, I could play it with no issue. I also attempted to copy directly through the autofs mount with just a cp to my home folder for a "large" (1.2GB) file. The copy was successful and quick (all 1.2GB received), but on playback, also stopped at the same point in time.

I'm using autofs to connect the two servers with these commands:
auto.master
/var/media /etc/auto.nfs

auto.nfs
tv 192.168.1.10:/var/media/tv
movies 192.168.1.10:/var/media/movies

192.168.1.10 is the server that houses the media and I can connect to it just fine, see all the files, etc. AutoFS appears to be "working" in that regard. As mentioned, large file copy across the network seemed to work, but I don't know what would cause file playback to stop midway or even stranger, why a file copied across the network would also stop playback while a file sftp'd across would play back correctly.

So I'm lost ... where can I look to find out any error messages or what the problem might be?

Edit: Adding a note - I tried to mount the filesystem across the network using:
mount 192.168.1.10:/var/media/tv ./tmp

That mounted fine, but had the exact same problem. So this appears to be more of a mount problem than an autofs problem (probably not surprising)

I also tried explicitly mounting with nfs4, which gives me the "file or directory does not exist" error, and I notice in nfsstat that the reads appear to be happening with nfs v2 (though there's no errors listed).

If anyone else runs into this, I found the answer.

I was about to just uninstall everything nfs-related and reinstall, when I noticed in Update Manager that two nfs packages were marked for possible upgrade. Figured I'd try that first. However ... strangely ... I couldn't actually select them for upgrade. Not sure why.

So I just did an apt-get install on both nfs-common and nfs-kernel-server (the two packages it wouldn't let me upgrade), which uninstalled portmap (among other things) and suddenly, with no other changes, everything worked.

I didn't have any strange missing upgrades on the client. So it seems there's an upgrade path broken for nfs from 10.04 to 12.04 in Ubuntu. Not planning on looking into it further than that, though (since it now works and was pretty simple to fix, though frustrating to find).