Adding monthly calendar shortcode twice results in blank page

Hi,

If i add the shortcode for the monthly calendar twice in a page on my website, the whole content area only the goes blank and there is no output at all, even the content above and below the shortcode is gone. Example: http://www.massagehuys.nl/deep-detox-massage/
I need to add it twice to show the current month's calendar as well as the next month. Do you have any idea how to solve this?

kind regards,

Hidde Braun, Amsterdam