First, LW Pro would indeed not affect anything on thr problem at hand AFAIK.

Next, have you tried playing said troublesome files on another player (Quicktime, anything?)?

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

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