ok, then

Sounds like there is only one of these listsboxes per form, and that this form is specifically designed for using a certain set of objects.
Assuming that, for the form class used for this type of form, add an object property to refer to this listbox. Set the reference in the listbox.init().
e.g.

** listbox.init()
** assume the thisform.oContactList property exists on the form
thisform.oContactList = this

in the code that triggers the change, refer to the form.oContactList instead of trying to find the listbox.
Since this is an object reference property, make sure you set it to .null. in the form.Destroy(), e.g.

** form.Destroy()
this.oContactList=.null.

HTH

>Sorry i was mistaken, the event is called from a programatic change event.
>There are two forms, one to search in and one to show details about the found record in the search form.
>
>The search form puts a nID_number in a textbox.value on the detail form.
>The programaticChange event from the textbox refreshes the form.
>
>For example, in the searchform you can look up the name of a person. The detailsform shows the details about this name (triggerd by the programaticchange event).
>
>The listbox is going to be used to list all contacts of this person.
>
>I'm afraid the techniques used (above) are not my choice.
>To throw the thing out and start over isn't an option. (yet)