I found a clean, simple solution that works beautifully posted by liuxihon:
I also had this problem, the next month, previous month links work, but date picker would give me “page not found error”.
It was due to the $link in the datepicker.php file.
Change $link .= ‘&eventDisplay=month&eventDate=’;
to $link .= ‘?eventDisplay=month&eventDate=’;
Worked for me XDDD.
The original post can be found here
liuxihon, you are brilliant! Your clean, simple fix worked like a charm.