Hi, i need help to solve this case, I'm trying to create login forms, and i got errors it said
"mysql_num_rows() expects parameter 1 to be resource, boolean given in line 18.

i can't figure out what this mean and how to solve it. here is code, please see line 18 in bold where it said

$count=mysql_num_rows($result);


Code:
ob_start(); 
// Connect to server and select databse.
include ('conn.php');
// Define $myusername and $mypassword
$myusername=$_POST['username'];
$mypassword=$_POST['password'];
// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
$sql="SELECT * FROM `members` WHERE username='$myusername' and password='$mypassword'";
//echo  $sql;

$result=mysql_query($sql);
// Mysql_num_row is counting table row
$count=mysql_num_rows($result);

// If result matched $myusername and $mypassword, table row must be 1 row

if($count==1){
// Register $myusername, $mypassword and redirect to file "login_success.php"
echo $myusername;
$_SESSION['myusername'] = $myusername;
//header("location:login_success.php");
}
else {
echo "";
//header("location:index.php?a='failed'");
}
ob_flush();
?>

can anyone help me what to write that code to solve this, because I'm still not get it.

thanks.

AM