Went through the latest guide, as setting up the UPnP sharing in 12 RC1 is very simple. It all "seemed" to work, as it library is viewable from the second XBMC computer. However, it will not play videos. The same videos play fine from the first XBMC that is sharing it's library out.
09:47:15 T:1120 NOTICE: DONE initializing playlistplayer
09:47:15 T:1120 NOTICE: CApplication::UpdateLibraries - Starting video library startup scan
09:47:15 T:1120 NOTICE: initialize done
09:47:15 T:4844 NOTICE: Thread CVideoInfoScanner start, auto delete: false
09:47:15 T:1120 NOTICE: Running the application...
09:47:15 T:2528 NOTICE: Thread Jobworker start, auto delete: true
09:47:15 T:1120 NOTICE: ES: Starting event server
09:47:15 T:4052 NOTICE: Thread CTCPServer start, auto delete: false
09:47:15 T:4844 NOTICE: VideoInfoScanner: Starting scan ..
09:47:15 T:3480 NOTICE: Thread CEventServer start, auto delete: false
09:47:15 T:3480 NOTICE: ES: Starting UDP Event server on 0.0.0.0:9777
09:47:15 T:3480 NOTICE: UDP: Listening on port 9777
09:47:15 T:4844 NOTICE: VideoInfoScanner: Finished scan. Scanning for video info took 00:00
09:47:15 T:2616 NOTICE: Thread CRssReader start, auto delete: false
09:47:15 T:3112 NOTICE: Thread Jobworker start, auto delete: true
09:47:17 T:5240 NOTICE: Thread Background Loader start, auto delete: false
09:47:49 T:5616 NOTICE: Previous line repeats 4 times.
09:47:49 T:5616 NOTICE: Thread Jobworker start, auto delete: true
09:47:52 T:1120 NOTICE: Previous line repeats 1 times.
09:47:52 T:1120 NOTICE: DVDPlayer: Opening: smb://public-pc/movies/Movies/(500) Days of Summer (2009)/(500) Days of Summer.avi
09:47:52 T:1120 WARNING: CDVDMessageQueue(player)::Put MSGQ_NOT_INITIALIZED
09:47:52 T:5368 NOTICE: Thread CDVDPlayer start, auto delete: false
09:47:52 T:5368 NOTICE: Creating InputStream
09:48:08 T:5368 ERROR: Couldn't connect to \\public-pc\movies, access denied
09:48:08 T:5368 ERROR: Couldn't connect to \\public-pc\movies, error code 86
09:48:08 T:5368 ERROR: CWINFileSMB: Unable to open file \\public-pc\movies\Movies\(500) Days of Summer (2009)\(500) Days of Summer.avi Error: 1326
09:48:08 T:5368 ERROR: CDVDPlayer::OpenInputStream - error opening [smb://public-pc/movies/Movies/(500) Days of Summer (2009)/(500) Days of Summer.avi]
09:48:08 T:5368 NOTICE: CDVDPlayer::OnExit()
09:48:08 T:5368 NOTICE: CDVDPlayer::OnExit() deleting input stream
09:48:08 T:1120 ERROR: Playlist Player: skipping unplayable item: 0, path [upnp://c41b095e-c5dc-ba98-6d84-7ce31474e2cc/videodb%3a%2f%2f1%2f2%2f1]
09:48:08 T:5212 NOTICE: Thread Background Loader start, auto delete: false
09:48:08 T:1120 NOTICE: CDVDPlayer::CloseFile()
09:48:08 T:1120 WARNING: CDVDMessageQueue(player)::Put MSGQ_NOT_INITIALIZED
09:48:08 T:1120 NOTICE: DVDPlayer: waiting for threads to exit
09:48:08 T:1120 NOTICE: DVDPlayer: finished waiting
09:48:41 T:1120 NOTICE: Storing total System Uptime
09:48:41 T:1120 NOTICE: Saving settings
09:48:41 T:1120 NOTICE: stop all
09:48:41 T:1120 NOTICE: ES: Stopping event server
09:48:41 T:1120 NOTICE: stopping upnp
09:48:42 T:1120 NOTICE: stopping zeroconf publishing
09:48:42 T:3480 NOTICE: ES: UDP Event server stopped
09:48:42 T:1120 NOTICE: stop sap announcement listener
09:48:42 T:1120 NOTICE: clean cached files!
09:48:42 T:1120 NOTICE: unload skin
09:48:42 T:1120 NOTICE: stop python
09:48:42 T:1120 NOTICE: stopped
09:48:42 T:1120 NOTICE: destroy
09:48:42 T:1120 NOTICE: closing down remote control service
09:48:42 T:1120 NOTICE: unload sections
09:48:42 T:1120 NOTICE: destroy
09:48:42 T:1120 WARNING: Attempted to remove window 10013 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10014 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10015 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10016 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10017 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10018 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10019 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10021 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10107 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10115 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10104 from the window manager when it didn't exist
09:48:42 T:1120 NOTICE: closing down remote control service
09:48:42 T:1120 NOTICE: unload sections
09:48:42 T:1120 NOTICE: application stopped...
09:47:15 T:1120 NOTICE: DONE initializing playlistplayer
09:47:15 T:1120 NOTICE: CApplication::UpdateLibraries - Starting video library startup scan
09:47:15 T:1120 NOTICE: initialize done
09:47:15 T:4844 NOTICE: Thread CVideoInfoScanner start, auto delete: false
09:47:15 T:1120 NOTICE: Running the application...
09:47:15 T:2528 NOTICE: Thread Jobworker start, auto delete: true
09:47:15 T:1120 NOTICE: ES: Starting event server
09:47:15 T:4052 NOTICE: Thread CTCPServer start, auto delete: false
09:47:15 T:4844 NOTICE: VideoInfoScanner: Starting scan ..
09:47:15 T:3480 NOTICE: Thread CEventServer start, auto delete: false
09:47:15 T:3480 NOTICE: ES: Starting UDP Event server on 0.0.0.0:9777
09:47:15 T:3480 NOTICE: UDP: Listening on port 9777
09:47:15 T:4844 NOTICE: VideoInfoScanner: Finished scan. Scanning for video info took 00:00
09:47:15 T:2616 NOTICE: Thread CRssReader start, auto delete: false
09:47:15 T:3112 NOTICE: Thread Jobworker start, auto delete: true
09:47:17 T:5240 NOTICE: Thread Background Loader start, auto delete: false
09:47:49 T:5616 NOTICE: Previous line repeats 4 times.
09:47:49 T:5616 NOTICE: Thread Jobworker start, auto delete: true
09:47:52 T:1120 NOTICE: Previous line repeats 1 times.
09:47:52 T:1120 NOTICE: DVDPlayer: Opening: smb://public-pc/movies/Movies/(500) Days of Summer (2009)/(500) Days of Summer.avi
09:47:52 T:1120 WARNING: CDVDMessageQueue(player)::Put MSGQ_NOT_INITIALIZED
09:47:52 T:5368 NOTICE: Thread CDVDPlayer start, auto delete: false
09:47:52 T:5368 NOTICE: Creating InputStream
09:48:08 T:5368 ERROR: Couldn't connect to \\public-pc\movies, access denied
09:48:08 T:5368 ERROR: Couldn't connect to \\public-pc\movies, error code 86
09:48:08 T:5368 ERROR: CWINFileSMB: Unable to open file \\public-pc\movies\Movies\(500) Days of Summer (2009)\(500) Days of Summer.avi Error: 1326
09:48:08 T:5368 ERROR: CDVDPlayer::OpenInputStream - error opening [smb://public-pc/movies/Movies/(500) Days of Summer (2009)/(500) Days of Summer.avi]
09:48:08 T:5368 NOTICE: CDVDPlayer::OnExit()
09:48:08 T:5368 NOTICE: CDVDPlayer::OnExit() deleting input stream
09:48:08 T:1120 ERROR: Playlist Player: skipping unplayable item: 0, path [upnp://c41b095e-c5dc-ba98-6d84-7ce31474e2cc/videodb%3a%2f%2f1%2f2%2f1]
09:48:08 T:5212 NOTICE: Thread Background Loader start, auto delete: false
09:48:08 T:1120 NOTICE: CDVDPlayer::CloseFile()
09:48:08 T:1120 WARNING: CDVDMessageQueue(player)::Put MSGQ_NOT_INITIALIZED
09:48:08 T:1120 NOTICE: DVDPlayer: waiting for threads to exit
09:48:08 T:1120 NOTICE: DVDPlayer: finished waiting
09:48:41 T:1120 NOTICE: Storing total System Uptime
09:48:41 T:1120 NOTICE: Saving settings
09:48:41 T:1120 NOTICE: stop all
09:48:41 T:1120 NOTICE: ES: Stopping event server
09:48:41 T:1120 NOTICE: stopping upnp
09:48:42 T:1120 NOTICE: stopping zeroconf publishing
09:48:42 T:3480 NOTICE: ES: UDP Event server stopped
09:48:42 T:1120 NOTICE: stop sap announcement listener
09:48:42 T:1120 NOTICE: clean cached files!
09:48:42 T:1120 NOTICE: unload skin
09:48:42 T:1120 NOTICE: stop python
09:48:42 T:1120 NOTICE: stopped
09:48:42 T:1120 NOTICE: destroy
09:48:42 T:1120 NOTICE: closing down remote control service
09:48:42 T:1120 NOTICE: unload sections
09:48:42 T:1120 NOTICE: destroy
09:48:42 T:1120 WARNING: Attempted to remove window 10013 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10014 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10015 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10016 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10017 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10018 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10019 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10021 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10107 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10115 from the window manager when it didn't exist
09:48:42 T:1120 WARNING: Attempted to remove window 10104 from the window manager when it didn't exist
09:48:42 T:1120 NOTICE: closing down remote control service
09:48:42 T:1120 NOTICE: unload sections
09:48:42 T:1120 NOTICE: application stopped...