Inserting media into a chapter- always possible?

Sometimes I can insert media (videos) into a chapter seamlessly. Othertimes it plays the alert tone and it won't allow me to- as if it's disabled in certain templates or I must follow a certain sequence of actions for it to work. I've had this problem for months. I've uninstalled/reinstalled and nothing has worked. I created a new project though and in that new project it works fine! Help?

-Adam