from the message, it appears that ZZKUNNR is a custom field attached to your MARA table. So, it is your System specific. I don't see ZZKUNNR available in MARA. If you look at the transaction code OMT3B (configuration for material master data screens), you can find K - Basic Data Screen in Maintenance Status field.
You may look in this area to fix your issue. Because yours is a custom field, its tough to analyse further.
Reward points, if it helps!
Regards
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