you forgot to include this code in your index.php /template
I'd like to just comment on this since I was stuck on this for a good 4 hours today, even after coming across and reading this thread repeatedly. I had to deal with a little learning curve myself. (I got it eventually figured out)
I also had the calendar error showing up on front-end editing as described above. What I didn't understand is that the front-end WYSIWYG is rendered in <jdoc:include type="component" /> in the template.
Since I had a unique homepage (using articles displayed on the homepage via modules, mod_placehere to be exact), there technically was no "component" on the homepage template (the divs that spit out of my template use conditional PHP statements), so I got the calendar error repeatedly.
Once I added the <jdoc:include type="component" /> into a div that was displayed on the homepage, the error went away.
One anomaly...since I have multiple modules displaying multiple articles on the homepage, and one component, regardless of which edit icon for whichever div you press, the WYSIWYG always shows up in the same place (I put it in the bottom right div), not sure if there's a workaround for this, but I can live with this behavior.