OK, I bit the bullet and went hardcore to try and track down this problem. To be honest it is so bad now that my wife is complaining and that is never a good thing!
ATV2, ethernet connection to NAS sharing via NFS. Using mysql for database sharing.
I uninstalled xbmc as per the instructions in the wiki, including removing the /private/var/mobile/Library/Preferences/XBMC directory.
Reinstalled gotham via command line.
Started Gotham, then quit
copied advancedsettings.xml and sources.xml to the userdata directory.
Updated to Gothan 13.1 Beta 2 via command line.
This should have given me a brand new, untouched install without any extra mods or setting changes.
Started xbmc.
Tried to watch lastest Big Bang Theory episode ... instant crash back to dashboard
Log -
http://xbmclogs.com/show.php?id=205027
I didn't have debug enabled, I will get another log with debug on.
Hate to labour the point, but that same error is there as the last line in the log again, just like every other time this has happened to me, but then I guess it could be a red herring.