Using the Rate Stretch Tool on 2/15 Build won't render

[JAkalaonu]

I was playing around with time ramping using the rate stretch tool with optical flow. I kept thing message everytime I tried to render.

System specs:

iMac (Retina 5K, 27-inch, 2020)
Processor 3.8 GHz 8-Core Intel Core i7
Memory 96 GB 2667 MHz DDR4
Startup Disk Macintosh HD
Graphics AMD Radeon Pro 5700 XT 16 GB