unable to move selected items from combobox to listbox

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C#3.5

i having a combo box in c# it is filled value from database sql server 2008,

i have ADD button,combo box and a list box ,My combo box in c# , is filled value from database sql server 2008,
When i select any item from combo box and press add button item can move from combo box to list box but it can not remove from combo box


shows error...Value does not fall within the expected range

code----

form load//

fillOffence(combobox1);//It fills the offence names

Add Button ////

string query = select [O_ID],[O_Desc] from tblOffence where O_Name'" +combobox1.Text.ToString() +"';
           DataTable dt = DataManager.GetDataText(query);
           foreach (DataRow dataRow in dt.Rows)
           {
               lstDesc.Items.Add(dt.Rows[0][1]);
               Global.Offence_id = Global.Offence_id + dt.Rows[0][1].ToString() + ;
error-->>        combobox1.Items.Remove(combobox1.SelectedItem);

               

           }