Using my rubbish German, I think the error is around an "Invalid Fieldname".
However, the useful information around which field and why, is not contained in this error message, so you'll need to dig around the ULS logs to find out what the actual issue is. Most likely you've created a column in Nintex Forms violates a rule of some kind, perhaps it already exists, or contains a special character. Have a look at your columns to make sure this is all correct, and then take a dive into the ULS logs if you can't resolve it, post the logs error on here and we'll try to help further.
I got the similar issue when I had javascript in the form,do u have any custom javascript? or just try revert back to previous version