Hi Tom.

When I change the -1 in the array to e.g. 1000, the displayvalue doesn't go empty at runtime so I think the '-1' is the problem.
Do negative values like this cause problems with comboboxes? Anyone an idea?

This is a known problem:

PRB: Negative Numbers Do Not Display in a Combo Box

Q190267


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The information in this article applies to:

Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0

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SYMPTOMS
If a combo box has the RowSourceType set to SQL Statement and the BoundTo property is set to true, negative numeric values do not display in the combo box.



STATUS
Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.



MORE INFORMATION
If the RowSourceType property is set to any other value, negative numbers will display in the combo box. Also, if the BoundTo property is set to false, negative numbers will display in the combo box, but the positive value of that number is written to the table.