I went to
Custom Layouts then
Event Edit Page.
For some unknown reason, these settings have been assign accidentally to «Category1».
«Event Edit Page» has now disappeared
So I choose the filter «Select Cateogory: Category1».
Now I open «Event Edit Page» and choose either «Category2» or «All categories» from the Category dropdown.
The message «You will loose any unsaved changes if you change the category. Do you wish to continue?» appears and I choose [OK].
As soon as I click [OK] a giant image will be displayed and on the bottom of this image you will find the message
An error has occurred.
500 Layout edit_ not found.
Return to Control Panel
See the attached screenshot.
It seems to be impossible to assign «Event Edit Page» back to all categories.
Thank you and kind regards
Chris