Need help troubleshooting a video offset problem

Hi all - I’ve successfully loaded a 62+ minute video into Dorico. When I try to put in the start offset (01:07:21:13) , the picture goes black and the sound is no longer there. Couldn’t be the offset is too long, could it?

Any ideas of how to solve this would be deeply appreciated. As always, thanks in advance for your time and any help offered.

I may be rusty reading SMPTE code, but haven’t you offset the video by one hour, seven minutes, twenty-one seconds, and thirteen frames? Is that longer than your music?