Stopping On Playback

I have 10 Macs and i have installed Premiere CS6 on all of them.

We have one issue, Once you have imported my video, i drop it on the time line and hit the space bar to play it. The video stops about a second after. I  hit the space bar again and it starts again then stops after a second or so ... and again and again .... and this happens on all of them !!

I'm pulling me hair out HELP !!

Many Thanks

Ryan