Insert Caption Greyed Out

I'm adding captions to a video, and everything seemed to be going well until the end of one video. When previewing the video in the closed caption editor it stops in the middle of one of the captions. I also can't add more closed captions as the Insert Caption button is greyed out and I can't split a caption as that option is greyed as well. 

I can still add captions to other slides just not any more to this one video. 

Any ideas on how to fix this?