Sorry guys I told you that I got the code from the wrong video. The right video is "Prevent Duplicates"

First, I would try to msgbox Combo22 to see what value is getting sent and ensure it is not in the table already.

Then I would look at where you are using it - in the "before update" event. In Richard's Prevent Duplicates video, he used in the click event, after access had already processed the change. if you move the code to the after update event, it should work but you can't cancel it per se. But after the msgbox you could add something like:

Combo22 = Combo22.OldValue
Combo22.SetFocus
Combo22.Dropdown

Michael, your screenshot shows DCount checking ColorT for the selected ColorID. If ColorT is your master list of colors, every valid selection already exists there, so it will be flagged even when it hasn't been added to the subform.

The check needs to count records in the table that stores the colors assigned to the current item, matching both that item's ID and the selected ColorID. When editing an existing row, exclude that row from the count. Also, in your BeforeUpdate event, the message alone doesn't stop the selection. Use Cancel = True when a duplicate is found.

What table supplies the subform, and what are its primary key and the field linking it to the main form? That will tell us which table and criteria belong in your DCount.

ColorSubFormSortQ is the query that supplies the sub form. The primary key is ID and the linked field is PartID.