Form not working for unknown reason

I spent whole day creating a form using different fields and once I want to send it – I have a general error message like “at least one field contains an error”. So I made all of the fields not mandatory but still I cannot send the form. I followed guidelines, checked field names, properties and everything – I cannot see what is wrong. Also on the list of all forms I see a notification that there is an error with configuration – yet no idea what is wrong. How to debug this? Please help…

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