>>>As i said before to another user, the problem is in the controlsource of the combobox. If i delete the actual controlsource and leave it empty the control works fine. The same if i insert a field of a table. I have the problem if i set as controlsource an object. In this case i set "ThisForm.oTab.IdZo".... ThisForm.oTab is a form's property structured like you can have if you make a scatter name ThisForm.oTab command....
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>>Аnd what is the value of ThisForm.oTab.IdZo? Is it filled with a number which exists in your combo's rowsource's bound column?
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>Yes. The value is correct and it is a number..

If the controlsource is a number that could be the issue.

Try to set BoundTo = .F.

From Help:
If BoundTo = .F.:
The Value property is determined by data type of the variable or field specified in the ControlSource property.

If the variable or field specified in the ControlSource property setting is of character type, the Value property is determined by the List property.

If the variable or field specified in the ControlSource property setting is of numeric type, the Value property uses the index number from the ListIndex property.