Unable to add transition: Bug causes crash or freeze.

When in iMovie adding transitions I've run into the issue of freezing upon reaching as certain point in the edit. The transition overlap is set to half and about halfway through the project upon attempting to add a transition i get a dialogue that "unable to add transition: not enough media" now this can not possiblly be true considering i am using photos all with a 4 sec duration. Alsoi after exiting out of this dialogue the application frezzes and keeps us from continuing an edit.

What can be done to rectify this?