Thank you for your quick response!
The template was set to a template that came with my theme. Setting it to default fixed the problem! Thank you very much!
Although, I have another issue. It is not critical, as I now use another widget that does the job, but it doesn’t work fully satisfying. The problem is that the widgets (all of them) doesn’t work with my site. When they are activated, they replace all the body text on single entry pages with the description for the next upcoming event. Is there any way to fix this?