So where exactly is this happening? From what you've described it sounds like the movie clip from the questionnaire "Neutral Film Clip_2.que" plays ok but then you never get to the first instruction item from "Mood Scale - after film, before smoking.que" -- is that correct?

If so, I have a couple questions. Let me ask first--is this condition the only one in which you access a filename that has a comma in it?

i.e.,

Mood Scale - after film, before smoking.que

If so, you might try it without the comma. If that makes no difference, the next thing I would try is to put the video clips on the local machine and see if it's a server related issue.