green screen in source window

As stated above, i sometimes get green screen in source window when playing an AMA linked mov file recorded on Canon 7D. After it happens once, all the clips become green screen, including the timeline window and fullscreen.

i get rid of the problem by restarting avid.

i play files from an USB3 hdd

i am using Avid MC 6.5.2

computer spec: Macbook pro retina 15", osx 10.8.4, itunes 11.0.4 (4)

thank u for your help :)