Add, creating a new for with the query as the record source works fine, including the Duration field, so I'm sure its not a simple spelling error.

ChatGPT:

✅ Explanation

The fact that the query works fine and a new form based on it displays the Duration field correctly tells us a lot:

The query itself is valid.

The alias name Duration is fine.

The expression Int([EndDateTime]-[StartDateTime]) is valid.

There’s no spelling or data type issue.


So the problem is not with your query — it’s with the existing form object.

Access forms store a hidden “field binding cache” internally.
When you change the Record Source of a form (especially from a table to a query that includes new calculated fields), Access doesn’t always refresh its internal field list.
As a result, the form simply doesn’t “know” about the new field, even though the query provides it — and that’s exactly when you see #Name?.

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🧰 Fix

You don’t need to rebuild the form.
Just force Access to refresh its field bindings:

Option 1 – Simple manual reset

1. Open the form in Design View.

2. Clear the Record Source property completely.

3. Save and close the form.

4. Reopen it in Design View.

5. Set the Record Source back to your query (BookingsQ).

6. Save again.

This forces Access to rebuild the internal field list.
After that, the Duration control will work as expected.

Option 2 – Do it in code If you want to trigger it dynamically (e.g., from VBA):

Me.RecordSource = "BookingsQ"
Me.Requery

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🧩 Summary

#Name? in this case doesn’t mean “bad expression” or “format problem” —
it means “Access hasn’t recognized the new field yet.”

That’s why:

> The same query works perfectly in a new form, but not in the old one.

Lars, I really appreciate your help and I've tried both suggestions but still this field (Now it's "Nights"), just will not work in the form. Some screenshots above. Peter

Peter Try deleting the field on the Form then re-add it.