iCal Calendar subscription 'refresh' problem, with 'invalid data' message

I have 'public' calendar subscriptions set up for my apple calendars because my work will not allow me to use iCloud functionality natively on my MBP. So I subscribe to the Apple calendars using the Apple calendar app on my MacBook.

When I changed MacBook I subscribed in the usual way but for one calendar, the most important, I got an error message stating that the calendar wouldn't be refreshed because "the data downloaded from [published iCloud calendar address] isn’t valid". The calendar subscription address is working on other computers, and works to enable me to subscribe to it on google calendar (which I don't use, but subscribed to test the address). Al the other calendar subscriptions work. I'm stumped. Any suggestions?