Calendar not syncing

Please try the following...

1. First check that all your settings are correct, that calendar syncing is checked on all devices (system preferences > iCloud on a mac and settings > iCloud on a iPhone, iPad or iPod).
2. Make sure the calendars you are using are in your 'iCloud' account and not an 'On My Mac', 'On My Phone' or other non iCloud account (you can do this by clicking/tapping the calendar button in the top left corner of the application ), non iCloud calendars will not sync.
3. If you are sure that everything is set up correctly and your calendars are in the iCloud account, you might try unchecking calendar syncing in the iCloud settings, restarting your device and then re-enabling calendar syncing settings.

I have this issue as well, and your suggestion did not help. I receive an error message "The server is currently unreachable or the connection was blocked." when opening Calendar on my rMBP. Disabling and enabling Calendar syncing in iCloud does nothing. However, the last time this came up - 6 months back or so - I did get an additional error message when I tried to re-enable the iCloud account which indicated the server security certificate was expired. (last time, I just instructed my MBP to ignore, seemed to clear things up) I'm not getting the "expired" thing this time. Sign in and sign out appears to be normal. I did check the security certificates in Keychain Access, and the server certificate did appear to be expired, so I deleted it. I had been told that I would automatically download a new certificate as a result, but that doesn't seemed to have occurred.

I'm still having the same issue though. For some reason, the server access is blocked on this one computer. IOS devices and iMacs in the house are all working fine.

Any thoughts? Thanks.

rMBP 15" (late 2013) OS X 10.10.5

Never mind. I signed out of iCloud, causing all kinds of things to be deleted from MBP, then restarted. Then I signed back in to iCloud and enabled Calendar again, causing error message that security certificates for the server were invalid. I clicked on "Show Certificate", and told MBP to "Always Trust", confirm change of insructions, and I'm back in business.