For example you are binding pricelist-objects to a combobox in WinForms application like this
cmbPricelist.DataSource = BL.GetPricelists();
cmbPricelist.ValueMember = "PricelistCode";
cmbPricelist.DisplayMember = "PricelistName";
and later you trying to get selected item from combobox like this
Pricelist p = (Pricelist)cmbPricelist.SelectedValue;
you might get an error "Unable to cast object of type 'system.string' to type..."
If you are using .NET Framework 4 Client profile ComboBox.SelectedValue method returns object (in this example Pricelist).
But if you are using .NET Framework 4 Full profile ComboBox.SelectedValue method returns ValueMember as String