I had the same problem. I fixed it by Mapping my video share in windows and then having xbmc use that mapped drive. I beleive that I was told that there was something screwed up with the SMB client in XBMC (at least in the windows version).
I had this problem also on anythign I played. I did the same thing ie mapped the source in Windows as a Network Drive, rather than use the SMB and now all works a treat.
Now I just got to work out how to use the Library properly!!