In my SS website (just updated to 2.4.10) I can't create some types of sup-pages. When I click the "create" button nothing happens and the console shows this error messages:

Refused to set unsafe header "Connection" base.js:65
Ajax.Request.Object.extend.setRequestHeaders base.js:65
Ajax.Request.Object.extend.request base.js:61
Ajax.Request.Object.extend.initialize base.js:59
(anonymous function) base.js:4
Ajax.SubmitForm base.js:80
addpageclass.form_submit cmsmain.js:17
POST http://example.com/admin/AddPageOptionsForm 500 (There has been an error) base.js:61
Ajax.Request.Object.extend.request base.js:61
Ajax.Request.Object.extend.initialize base.js:59
(anonymous function) base.js:4
Ajax.SubmitForm base.js:80
addpageclass.form_submit

I've found other threads reporting this issue but some are unsolved and the others didn't help in my situation. I am wondering why some pagetypes I can create and this particular pagetype not.My PHP code ins't that much different. There are just a lot of fields in this pagetype and nothing special when loading (see attached php file).

Any help is appreciated! Couldn't find a solution the last 4 hours …