I write this code :

MyCombo.Selecte dIndex = MyCombo.Items.I ndexOf ("MyString")

this line return -1 as the index value ( it means MyString is not found)

"MyString" exists in the items list. MyCombo is filled with the following code :

MyCombo.DataSou rce = MyDataSet.table s
MyCombo.Display Member = "...."
MyCombo.ValueMe mber = "...."...