Does the record get deleted even though you get this message?
Are you using a script to delete the record or selecting "delete record" from the records menu? (or using the keyboard shortcut for it.)
Is there an OnRecordLoad trigger set for the layout where you attempt deleting the record?
The record does not get deleted.
No script to delete just the delete record button up on top.
No OnRecordLoad Trigger just a trigger on Layout Enter that is to sort records and resize the window.
I've been able to replicate this in a small test.
Here's what I did.
I related a table to itself in a self join. The self join isnot the issue but it made for a quicker test.
In the relationship, I enabled the "Delete Related Records in this table when a record is deleted in the other table". The "other table" being the table occurrence listed for the layout where I would delete a record.
I then clicked on the fields tab and deleted a field used in this relationship.
When I attempt to delete a record, I get the results you report.
This suggests that you have a relationship with this "delete" option specified, but that one of the fields used in the relationship has been deleted from the table.
Unfortunately for you, you have a lot of different relationships to double check to see which one includes these two features: a missing match field and the "delete" option selected.