error in checkbox coding

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ASP.NET

ii want to store multiple selected checkbox in database...so m using below code:-

string selectedItems = string.Empty;
        foreach (ListItem item in this.CheckBox1.Items)
        {
            if (item.Selected)
                selectedItems += item + ",";
        }
        SqlCommand cmd = new SqlCommand("Insert into Candidates(Candidate_Pref_Job_Cat) values('" + selectedItems + "')", cn);
        cn.Open(); // I am assuming that you have written down the connection string.
        int iCount = cmd.ExecuteNonQuery();
        cn.Close();

bt error is:- does not contain a definition for 'CheckBox1' and no extension method 'CheckBox1' accepting a first argument of type could be found....

m using single checkbox nd use Repeater Control to display multiple checkbox....so how to declare checkbox in my code??????or what is error in code????