I've tried several themes with the same result. When viewing a month with no events, I get the following errors all over the page...
Warning: in_array() [function.in-array]: Wrong datatype for second argument in /homepages/xxxeditedoutxxx/wp-includes/post-template.php on line 1039
If you click over to a month with events the errors are still there, but with a refresh on the page and they go away. Clicking to another month with no events and the reverse - no errors unless you refresh and then they re-appear.
Running WP 3.5. Any ideas?