I have a very simple rule to set Original Estimate based on the sum of a couple custom fields. It is failing saying that Time Tracking is not available:

All searches on this site that are similar say that Time Tracking needs to be available on the screen, but it is and so is Original Estimate. I can manually set the value and log time.

Here is the simple rule:

Am I missing something obvious? Any suggestions would be greatly appreciated.
Thanks.