The application “Calendar.app” is not open anymore.

Hi,

I had just put in several new calendar entries. Then I closed the app. When I tried to open it again it kept bouncing. I tried to force close it, but it just sits there the Force Close is still available.

I found it in finder and when I open the app I get the pop up: The application “Calendar.app” is not open anymore.

I also have the app on my iPhone 7 as well as my iPad. They are still working.

MacBook Pro (13-inch, Mid 2012)

macOS High Sierra ver. 10.13.3

Processor 2.5 GHz Intel Core i5

Memory 4GB 1600 MHz DDR3