sivann

1) Inside htdocs/wp-content/plugins/calendar-posts:
Edit file calendar-posts.php (make a backup first)
comment out or delete line ~65 (where it includes jquery-1.4….)
Because jquery is included also elsewhere, the correct jquery will be included now.

If not fixed, then:
2a) Inside htdocs/wp-content/plugins/calendar-posts/jquery.datepick.package/
put jquery-1.6.1.min.js (download from http://code.jquery.com/jquery-1.6.1.min.js)

2b)
change line 65 of calendar-posts.php file, to include the new jquery version instead of 1.4.

Just updating the inclued jquery to 1.6.1 seems to fix the errors.