error in reading excel data?

I am reading the excel data when the excel file uploading and save the excel content in my db.

now i get this error , how to rectify this error

The Microsoft Jet database engine could not find the object '$Sheet1'.  Make sure the object exists and that you spell its name and the path name correctly.

code:

 else if (extn.Equals(".xls"))
            {
                string filePath = Server.MapPath("uploads/" + filename);
                //string connstring = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + filePath + ";Extended Properties='Excel 8.0;HDR=NO;IMEX=1';";   // Extra blank space cannot appear in Office 2007 and the last version. And we need to pay attention on semicolon.

                string connstring = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + filePath + ";Extended Properties='Excel 8.0;HDR=Yes;IMEX=1';";
                    //Extended Properties='Excel 8.0;HDR=NO;IMEX=1';";  //This connection string is appropriate for Office 2007 and the older version. We can select the most suitable connection string according to Office version or our program.

                   using(OleDbConnection conn = new OleDbConnection(connstring))
                   {
                       conn.Open();
                       DataTable sheetsName = conn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables,new object[]{null,null,null,"Table"});  //Get All Sheets Name
                       string firstSheetName = sheetsName.Rows[0][2].ToString();   //Get the First Sheet Name
                       string sql = string.Format("SELECT * FROM [$Sheet1],firstSheetName");  //Query String
                       OleDbDataAdapter ada =new OleDbDataAdapter(sql,connstring);
                       DataSet set = new DataSet();
                       ada.Fill(set);
                       //set.Tables[0];  
                   }

query = @"INSERT INTO Fileupload([category],[subcategory],[uid],[oid],[up_name],[demo1],[keyword],[fdata],[aflag],sizebyte)
VALUES(@category,@subcategory,@uid,@oid,@up_name,@demo1,@keyword,@fdata,1,@sizebyte)  ";
                SqlCommand command = new SqlCommand(query, con);
                //command.CommandText = command.CommandText.ToString();
                command.Parameters.AddWithValue("@category", dropcategory.SelectedValue.ToString());
                command.Parameters.AddWithValue("@subcategory", DropDownList1.SelectedValue.ToString());
                command.Parameters.AddWithValue("@uid", Session["user_id"].ToString());
                command.Parameters.AddWithValue("@oid", txtOwnerId.SelectedItem.ToString());
                command.Parameters.AddWithValue("@up_name", fname);
                command.Parameters.AddWithValue("@demo1", demo1.Text);
                command.Parameters.AddWithValue("@keyword", key);
                command.Parameters.AddWithValue("@fdata", );
                command.Parameters.AddWithValue("@sizebyte", size);
                command.ExecuteNonQuery();

            }