[Ted Martin] “Could this be a Quicktime issue?”
Mac dropped Quicktime a long time back. It uses AV Foundation now.
If it’s failing on two different files and on an old computer with an old OS you have a serious underlying problem.
This is especially so if a file that worked last year isn’t working this year.
Please make sure you’re testing and reporting correctly because seeing this on a computer with Lion as well doesn’t make sense.
[Ted Martin] “3. plenty of drive space with no RAM issues that I can see”
Sorry but subjective comments can’t really be evaluated. Given your description something is wrong and your description seem incongruous at this point.
Please read the sticky post at the top of this forum.