My wife had the exact same problem after I updated her laptop to the latest version of Quicktime. Tech support told her that the math lab software doesn’t work with the newest version, so she had to uninstall it and then go back and install the older version. That fixed it.
I believe the version you need is 7.60.92.0
Thank you so much! I am working on uninstalling the newest Quicktime and finding the 7.60.92.0.