How to add contents from RadEditor into Gridview using Session?

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C#

C#4.0

I have written code on ButtonClick event of the btnAdd but it's not working. its giving an exception as:


Input string was not in a correct format.Couldn't store <<span style="font-size: 22px;">asdfghjkl> in Description Column. Expected type is Single.


My Code is:

protected void btnAdd_Click(object sender, EventArgs e)
        {
            if (txtModuleName.Text == "")
            {
                ScriptManager.RegisterStartupScript(UpdatePanel8, typeof(string), "alertscript", "alert('Please Enter the Module Name')", true);
            }
            else if (RadEditor2.Content == "")
            {
                ScriptManager.RegisterStartupScript(UpdatePanel6, typeof(string), "alertscript", "alert('Please Enter the Description')", true);
            }
            else
            {
                string modulename = txtModuleName.Text;
                string description = RadEditor2.Content;

                
                DataTable dt1 = (DataTable)Session["Project"];
                DataRow row1 = dt1.NewRow();
                row1["ModuleName"] = txtModuleName.Text;
                row1["Description"] = RadEditor2.Content;
                
                dt1.Rows.Add(row1);
                GridView1.DataSource = dt1;
                GridView1.DataBind();
                txtModuleName.Text = "";
                RadEditor2.Content = "";
            }
        }