Mysql fatal error during command execution

public DataSet GetTotalAmountDetailsDB(NewPhotoViewModel npvm)
{
MySqlConnection con = new MySqlConnection(ConStr);
string cmdstr = "SELECT n.Price FROM (SELECT @rownum + 1 r, Price,Quantity FROM printmaster WHERE Quantity >= 13 And size='4*4' ORDER BY Quantity) n, (SELECT @rownum := 0) r WHERE r = 1 LIMIT 1";
MySqlCommand cmd = new MySqlCommand(cmdstr, con);
DataSet ds = new DataSet();
MySqlDataAdapter da = new MySqlDataAdapter(cmd);
da.Fill(ds);

return ds;
}


when i executing the querry i encountered Mysql fatal error during command execution. Is there any wrong in this querry.... plz help me....