Why does my 'Delete Case' action in the case search report not work?
It has to do with an added custom field. See: 
Its a range and an option list.
Workaround.

Go to the custom field definition (it's somewhere on cases, for techies, you can find the id in the javascript error.
Change the Field Input Type to Single Line Input Field
Now Search by Range is visible. Uncheck it.
Set the 'Field Input Type' back to the former value.
And save.

The case report should by back to normal.