The problem is the table definition - you're asking SQL Server to delete a row ... but there isn't enough information for it to know which row you want deleted.
I get that. So why would it not just delete both rows?

What you should do is add another field to the table to act as a unique key
I can do that. I have actually had those, in the past, but I never could figure out what the usage would be, in this type of table and used the way this table is used. But with the issue as you describe, I can readily see where an integered numbered, primary key field that is used for nothing else would resolve that.

Maybe I'm missing something, but this doesn't seem that complicated, and I'm not convinced that any code is directly at fault here. I think the fault is that you seem to not have a Primary Key defined for this table, which would have prevented you from creating a duplicate row like this.
That is true. I intentionally have no primary key, as all of the data in the 3 fields will be duplicated.

Locate the duplicate row, right-click that row, and choose delete.
I did that. The table will not allow me to delete either of the rows. That is when the error message displays.

-If that doesn't work, then try modifying the fields in this row so that it is no longer a "duplicate",
Tried that too. It will now let me do that. Short of rebuilding the table, I have found no way to eliminate the extra row.

I think that what I will do, based on your input, is to create a self-filling integer primary key field. However, until I can eliminate the duplicate row, the table won't let me do anything (not true, I can do anything I would normally do with the table, except alter/delete either of the duplicate rows. And whatever I do with either of the two records is not accepted by the table.

I am very unfamiliar with this database. I have been using ACCESS. In ACCESS this field was automatically generated in any table I built. How do I make this primary field self-generate when I create a new record?

So, short of just junking the table and rebuilding it, is there a way that I can deal with the duplicate row? Junking the table would not be a big deal, but I would like to be able to know how to fix this, when I inevitably do this again.