PHp - submit page returns Internal Server Error

I'm making a flat file login system and when I click the submit the button on the login.php page it goes to protected.php and returns Internal Server Error, but when I just load the protected.php page without using the form everything turns out fine.

<html>
    <link rel="stylesheet" type="text/css" href="style.css">
    <body>
        <center><img src="logo.png"></center>
        <div id="login">
            <form action="protected.php" method="post">
            </br>
            Username  <input type="text" name="user" class="text"/>
            <p></p>
            Password <input type="password"" name="pass" class="text" />
            <p></p>
                <input type="submit" value="Login" class="button">
            </form>
        </div>
    </body>
</html>

protected.php

<?php
$usr = "admin";
$pass = "admin";

$iusr = $_POST["user"];
$ipass = $_POST["pass"];

if ($iuser !== $usr || $ipass !== $ipass) {
?>
<html>
<script type="text/javascript">
<!--
window.location = "login.php"
//-->
</script>
</html>
<?php
}
?>
<html>
    <link rel="stylesheet" type="text/css" href="style.css">
    <body>

    </body>
</html>

Please help! Thanks in advance!

Solution

The "Internal Server Error" could mean several things, but most likely means an error in your PHP code. This will require setting the display_errors property to "1" in your php.ini. The problem might also be a startup error, so you may wish to also consider the display_startup_errors property.

http://www.php.net/manual/en/errorfunc.configuration.php#ini.display-errors

Two comments about the code, unrelated to your question: 1) the expression $ipass !== $ipass seems like a typo, as it will always return FALSE, and 2) this "security" is easily bypassed by turning javascript off. Consider using header() for redirects instead.

https://www.php.net/manual/en/function.header.php

EDIT: ... in this specific case, the error is use of the variable $iuser, which is undefined. You'd previously declared it as $iusr. Turning on error reporting or looking at the log will present you with good error messages to find these sorts of problems easily.