[PROBLEM] freezing hi-def movies

[scard]

hi guys, i just bought myself a rasp pi and installed xbian alpha 5 on a sdcard.
Xbian runs relatively smooth, although crashes occasionally (something to do with cec plugin i think)

my problem is, when i try to play movies which i have added to the library from my 1tb ext hdd ...it plays for 5-15 seconds and then freezes as if it was streaming. This forces me to press stop which returns me to the main menu, however if i wait, it returns to the main menu itself. Essentially i cannot use the pi for what i originally intended - playing movies lol.

build - latest
connected via hdmi - 50hz at 1080p. / vsync decided by software /
wireless remote/trackpad
xbian on 32gb sdcard 10
local media - 1tb external ntfs hdd (usb0)
file format -mkv
overclock setting - xbian
xbmc displaying at 720p

streaming files seems to work, no problem thankfully, however it would be great if my local files would also work.

thanks for all your hard work guys.. much appreciated
scard