Yosemite Calendar v8: "You don’t have permission to modify this event."

[JohnDohe]

I'm getting the following message when I right-click on a day in Calendar version 8.0 and select "New event":

"You don’t have permission to modify this event."
"The owner of this calendar doesn't allow you to create these items."

What to do??

HALP !!!

 

[Eithanius]

The last time I got this error message on Calendar is when my Contact list is empty...