Having spent the last several days poking around the forums in search of a clue about fixing my problem, I came across this discussion of the permalinks bug and proper display of the calendar: http://wordpress.org/support/topic/354580?replies=27.
I tried tweaking the permalinks as suggested in that thread, to no avail, BUT I did discover that when I reverted to default permalink setting, all links and displays worked correctly. They won’t work with any custom permalinks, however–even after I replaced the datepicker.php as suggested.
So I tried deleting the plugin entirely, set the permalinks with the desired custom structure (/index.php/%year%/%postname%/) and reinstalled the plugin.
No dice. Argh!
So… any thoughts on what’s happening here, and how I can fix it??
