Error when getting the folderpath from server.mathpath

string FileName = lblFileName.Text;
string Extension = Path.GetExtension(FileName);
string FolderPath = Server.MapPath(ConfigurationManager.AppSettings["FolderPath"]);
string CommandText = "";

switch (Extension)
{
    case ".xls": //Excel 97-03
        CommandText = "Questionnaire.spx_ImportFromExcel03";
        break;
    case ".xlsx": //Excel 07
        CommandText = "Questionnaire.spx_ImportFromExcel07";
        break;
}

//Read Excel Sheet using Stored Procedure
//And import the data into Database Table
String strConnString = ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString;
SqlConnection con = new SqlConnection(strConnString);
SqlCommand cmd = new SqlCommand();
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = CommandText;
cmd.Parameters.Add("@SheetName", SqlDbType.VarChar).Value =  ddlSheets.SelectedItem.Text;
cmd.Parameters.Add("@FilePath", SqlDbType.VarChar).Value = FolderPath + FileName;
cmd.Parameters.Add("@HDR", SqlDbType.VarChar).Value = rbHDR.SelectedItem.Text;
cmd.Parameters.Add("@TableName", SqlDbType.VarChar).Value = txtTable.Text;
cmd.Connection = con;

try
{
    con.Open();
    object count = cmd.ExecuteNonQuery();
}

catch (Exception ex)
{
    lblMessage.Text = ex.Message;
}
finally
{
    con.Close();
    con.Dispose();
}

C:Visual StudioTestTestTestAdminFilesExcel07.xlsx

C:\Visual Studio\Test\Test\Test\Admin\Files\Excel07.xlsx

string FolderPath = "C:\Visual Studio\Test\Test\Test\Admin\Files\Excel07.xlsx";