Medialab won't play wmv files

I'm trying to get Medialab to play some short .wmv files (tv ads). I converted .flv files from youtube to .wmv files using Replay Converter (applian.com).
I've inserted them as movie items in questionnaires. But when I try to
run the questionnaire, a black rectangle appears, turns to white, then
Medialab just freezes - video doesn't present and I have to use
windows task manager to get out of Medialab. I've checked and the
videos do play in Windows Media Player with no problem. I'm running
Medialab 2006.2.40

Any idea what the problem is and how to fix it?

Thanks,
Amara

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