movie editing

While editing the movie, the video freezes after a few minutes of work. Each time I have to close Camtasia and reopen it again. In he doubt if this is a problem of my computer (Mac 12.3.1) I have verified that with other applications (like FinalCut) this problem doesn't happen. There are no other applications running at the same time, and I clear the RAM but this does not solve the problem.