Error "Undefined index:" sending contact form

I have restored a backup of a contact form from another site to an new site, made some changes.
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On test I receive this error:
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Sie haben nicht das richtige Bild gewählt.
(translated You didn't choose the right image)

Notice: Undefined index: name in /homepages/37/d33287505/htdocs/joomla_live/libraries/cegcore2/admin/extensions/chronofc/functions/validate_fields/validate_fields_output.php on line 95
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The correct Image is selected, I don't want to use a database.
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I can not find the reason.
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Regards
Peter

Hi Peter,
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Maybe this is a small bug, you can disable the security image validation or wait for the new update!
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Best regards

Hi Max,
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It happens only when I add the form inside an item with {chronoforms6}kontaktformular{/chronoforms6}.
Directly called as menu item it works well.
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I need the security image and I don't want to use google recaptcha (not tested if this would work)
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Peter