Error in JS console which prevents Calendar to be loaded in some cases

STEPS TO REPRODUCE

1. Insert Calendar Macro in a page
2. Save the page
3. Hit CTRL + F5 (if the case) and observe the browser's JS console

EXPECTED RESULTS

Calendar macro is displayed properly.

ACTUAL RESULTS

The calendar is not loaded. In browser's JS console there is the following error:

Sometimes, when just navigating to the page containing the Calendar macro, it seems to loaded properly, but after a refresh the error occurs again.