Hi Mogens,
It sounds like there are some code conflicts on your site. To help troubleshoot, can you log into your premium account on this site and post this issue in a Premium Support forum? This forum here is the “Pre-Sales Questions” forum, and since you are not posting from a logged-in account I cannot verify that you have a license.
If you do not have a premium license, please post in our free support forums here → http://wordpress.org/plugins/the-events-calendar
Thank you!
George