Cannot preview or export mp4 video from Hype 3.5.2

Hi, I have a short 5-second animation containing a static background png, one text field and three animated png images.

The animation plays fine in Hype 3.5.2, but will not preview anywhere or export (I need an mp4 video).

Are there any known issues with this Hype version, or am I doing something wrong within the attached file? (2.3 MB)

My iMac has plenty of free memory left ( > 4GB).

Thanks in advance - any useful advice will be much appreciated!

After much trial and error, I discovered the problem was caused by an incorrectly configured Custom CSS font!