I have had similar probs with build 279, which I just installed about an hour ago. I made no changes in my setup of any kind.
Playing only vbr hi mp3s from a "random" smartlist. 21k files in playlist.
Behavior: Start play, MC plays a song or 2 and hangs after cutting the last 5 secs off the song. Hit play/pause a couple of times and pb resumes with the next song but with the cover art of the previous song. After a minute or 2 of playing again, MC just stutters and I get the following error message: "Internal play buffer error: playing buffer accumulated too much spent data".
I have gone back build 276 and everything (except the ATI RW mentioned in another thread) is ok.
Media Center Registered 11.0.276 -- C:\Program Files\J River\Media Center 11\
Microsoft Windows 2000 5.0 Service Pack 4 (Build 2195)
AMD Athlon 1647 MHz MMX / Memory: Total - 523 MB, Free - 319 MB
Internet Explorer: 6.0.2800.1106 / ComCtl32.dll: 5.81 / Shlwapi.dll: 6.00.2800.1612 (xpsp2.041207-1145) / Shell32.dll: 5.00.3900.7032 / wnaspi32.dll: N/A