I ran into the same WordPress SEO by Yoast conflict on my WP 3.4.1 site.
Since I was running the std version of the calendar plugin then Initially I tried upgrading to "Free 1.8 RC-2.zip" but this did not resolve the conflict, so I then tried "Premium 1.8 RC-2.zip" and this did successfully resolve the SEO plugin conflict.
However, now that I'm running with the Premium 1.8 RC-2 I now notice that when "Hide Google Maps until clicked" is NOT checked then the small Google Maps are no longer visible for each event (although the full Google Map displays OK when I click an event's "View Full-Size Map" button). But, if I then check the "Hide Google Maps until clicked" then I can no longer click to display even the larger Google Map).
One minor unrelated comment on the calendar plugin is that it would be nice to able to opt to NOT to display the PRINT button on the Agenda page.
In spite of these issues I still like this calendar plugin. When you do finalize the next release of the plugin can you please include upgrade instructions for those of us who are running the Premium 1.8 RC-2 temp release? (if it is different than a standard upgrade)
P.S. I was thinking after-the-fact that since the Yoast SEO conflict was merely a display issue related to the data entry of SEO parameters then instead of upgrading to the calendar's RC-2 fix I could probably have stayed with the current release of the then.ly plugin and instead simply 1) deactivated the then.ly plugin, 2) entered my Yoast SEO parameters, and 3) re-activated the then.ly plugin and all would have continued to function properly for both the calendar and the Yoast plugins... but this is just a theory as I did not try it.