Disclaimer, I am not a mac savy guy!
Mac Pro running 10.4.7. User has 3 .AVI files that lock up Quicktime when she attempts to open them, other .avi files and .mov files play OK. I have copied the 3 .avi files to another mac and they open OK. Tried re-installing Quicktime and the problem remains. The only other thing I can think of is to completely uninstall Quicktime, restart, and then do a clean install of Quicktime but I am unable to figure out how to do a complete uninstall. This user also has Final Cut Pro installed, will uninstalling Quicktime cause a problem for Final Cut Pro? If anyone has an answer for this, or a better idea for troubleshooting, I'd love to hear suggestions. Thanks.