Calendar - "The server responded with an error"

Hello folks,

I use Calendar and iCloud for years and all was syncing well, on all my devices: iPhone X, MacBook Air and iMac.

Today, I believe since 4 hours ago, I noted changes I made on the iMac Calendar, didn't show on iPhone and I got a message from Calendar: "The server responded with an error".

Well, I thought it could be my iMac, which runs with High Sierra, although it never has shown any problems, so I restarted it but problems remained.

I made the changes on iPhone Calendar, but still no results. No syncing.

I went to MacBook Air and made the Calendar changes there and moments later the same message received in the iMac: "The server responded with an error", thus I understood the problem wasn't on my iMac.

I noted Photos is syncing, but calendar not.

Any suggestion will be very welcome

Paulo