Thanks Brook for the Tip!
I deactivated all plug ins to research if this there is the problem and tried to activate them and test after every plug in. It turns out that it was working again with all deactivated plug ins. I could activate them all again and it is still working. Problem solved.
Hi Sanjog,
Sorry for the late answer. I had to check some details with my provider. It seems that it is a rights problem. I am the admin but when I download pictures in WordPress the pictures end up not editable what is weird. So all is well with Sydney. Thanks for your willingness to help.
Hi Brian. I was tired and landed in the wrong support forum. The events calender works just fine now. You can delete this if it is possible