Hi MattMerrill,
This error is from a significantly older version of the editor. Additionally, Sequencer has replaced matinee. Because you are experiencing this error in Sequencer, it would be best to open a new answerhub post. In your post, please include what steps you are taking to reproduce this error on your end along with whether or not this occurs in a clean, blank project with no additional content or if it is limited to one project. I am closing this thread as outdated.