A super quick article on resolving this issue if it ever appears again.
Why?
At time of print, this error was happening to schedules in Zoho Books, Zoho Inventory, and Zoho Subscriptions. Unless you can monitor when these type of schedules are failing, you won't see this error until you go in and try to save it again.
How?
The super quick answer is remove any spaces from the name of the schedule.
The longer answer is demonstrated in the following screenshots:
Error:
Solution