Onedrop Ajax Form - Error


I got a problem. I am runing the onedrop/ajaxform package on one of my sites (
Out of some reasons I get en error on submitting the Ajax Form. I get the following error:

Something went wrong with the ajax form request

The error should be in the form.js
With the Chrome Development tool I got so far that the “formData” could not be read.

Maybe someone of you can help me.

Thanks, David

Which version of Neos and which version of our AjaxForm package are you using?