Same problem as many – double pages. Thesis 1.8.3, upgrading from Cal 1.2.2 to Cal 2.0.5.
My process: I uninstalled old Cal version and installed new Cal and then Pro pack. Tried all of the templates in the Cal settings with no luck. They all screwed up the page layout. Started looking at the base CSS files and discovered an issue that fixed it for me and maybe others will benefit.
Apparently the install of Cal 2.0 didn’t replace many .php & .css files in the /themes/thesis/events directory. I replaced the following files with files straight out of the Cal 2.0 zip file;
events-list-load-widget-display.php
events.css
gridview.php
list.php
single.php
Everything now works and looks fine. None of the coding fixes in this thread were necessary.