I had an issue with using this plugin and an archive.php page, where on line 74 of my-calendar-core.php $this_post->ID was not defined (presumably because the nature of the query object is a bit different for archives?). I resolved by editing that line to:
if( isset($this_post->ID) ) $id = $this_post->ID;
Also perhaps worth noting, I am seeing warnings along these lines (I see them through debug bar plugin):
WARNING: wp-content/plugins/my-calendar/my-calendar-core.php:82 - in_array() [function.in-array]: Wrong datatype for second argument WARNING: wp-content/plugins/my-calendar/my-calendar-core.php:939 - in_array() [function.in-array]: Wrong datatype for second argument WARNING: wp-content/plugins/my-calendar/my-calendar-core.php:228 - in_array() [function.in-array]: Wrong datatype for second argument
and numerous notices along these lines (just quote one for example):
NOTICE: wp-content/plugins/my-calendar/my-calendar-core.php:82 - Undefined variable: array
I'm not sure to what extent, if any, these messages pose a problem but my functionality seems ok.