My solution was to test to see if the control had focus before updating the control property,
Here I am updating a combo box search to a wild card search
Private Sub Combo_Change()
'Note control passed to after update sub, then returns to change sub where error occurs
'Combo is the name of your combo box
If (Combo Is Me.ActiveControl) Then
Me.Combo.RowSource = _
"SELECT [CCL sites v Contract No].ContractID, [CCL Sites].[Site Address], [CCL sites v Contract No].[Contract No] " & _
"FROM [CCL sites v Contract No] INNER JOIN [CCL Sites] ON [CCL sites v Contract No].SiteID = [CCL Sites].SiteID " & _
"WHERE [CCL Sites].[Site Address] LIKE '*" & Me.Combo.Text & "*' " & _
"ORDER BY [CCL Sites].[Site Address]"
Me.Combo.Dropdown
End If
End Sub