I'm stuck in a form.

In the attachments I have uploaded a print screen of the issue.

When I select "Selecteer opdrachtnummer" the value in "Kenteken" has to be filled in.

When "Kenteken" is filled in the field under it has to set a variable.

The field "Kenteken" in the sub-form "Kosten" is based on the field "Kenteken."

The problem is:

Why does "Kenteken" right in the top doesn't fill in his value. Probarly there is a value because the field "Kenteken" in the sub-form is based on it.