I'm having a lot of trouble here. All I want to do is be able to make a selection with the mouse and remove it from the timeline on both the audio and video tracks. Sometimes it works and sometimes it doesn't. I'll highlight what I want to remove, and hit either cut or delete. The first time it worked, it removed that section of the audio and video and left a blank gap in the timeline just like i wanted. However, when I tried to do it again on a diff selection, it woulnd't work,, why is this?