We saw this error last week too for several days, then it went back to working without our changing anything. We heard from a Google rep "that a change is currently rolling out that removes support for unlimited duration, and the maximum will be 540 days. It's already been changed in serving (unlimited duration is treated as 540 days) but the UI and API are now being updated to match."
Hoping that there is some announcement about what to expect and when this change may be formally made!