While working with my Google Calendar just now, although I was able to view my calendar and create new events with no problem, when I tried to edit an existing event, I was getting an “Unable to reach Google Tasks” error displayed in the bottom-right corner, and the “edit event” page would not appear.
Logging out of my Google account and then back in again worked around this issue for me; editing events on my calendar works fine now for me after doing that.