500 Internal Server Error when I do a Include : <p>I'm trying to do an include in php, but when I execute the form submit Internal Server Error appears. If I delete the include this error does not appears. </p>

<p>I've tryed to change permissions and the owner of the forlders and files to www-data: but it doesn't work. </p>

<pre><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;

&lt;head&gt;
&lt;title&gt;
    registro.
&lt;/title&gt;
&lt;meta charset="utf-8"&gt;
&lt;script src="jquery.js"&gt;&lt;/script&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;form action="#" method="post"&gt;
    &lt;label for="user"&gt;Nombre de usuario:&lt;/label&gt;&lt;input name="usuario" id="user" type="text"&gt;&lt;br&gt;
    &lt;label for="pass1"&gt;Contraseña:&lt;/label&gt;&lt;input name="pass1" id="pass1" type="text"&gt;&lt;br&gt;
    &lt;label for="pass2"&gt;Repita Contraseña&lt;/label&gt; &lt;input name="pass2" id="pass2" type="text"&gt;&lt;br&gt;
    &lt;input type="submit" value="enviar"&gt;
&lt;/form&gt;
&lt;?php
if($_POST){
    $user=$_POST['usuario'];
    $pass1=$_POST['pass1'];
    $pass2=$_POST['pass2'];
    echo $pass1;
    if(is_null($user)|| is_null($pass1)||is_null($pass2)){
        echo 'Error, alguno de los datos no es válido';
    }else{
        if($pass1==$pass2){

            include 'conexion.php';
            $mysqli -&gt; query("INSERT INTO USERS VALUES ('2','2')");
            echo 'Realizado correctamente, Redirigiendo a pagina principal...';
            header ("refresh :2,url=login.php");
        }else{
            echo 'Error, las contraseñas no coinciden';
        }
    }

}
?&gt;
&lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>this is the mensage:
Internal Server Error</p>

<p>The server encountered an internal error or misconfiguration and was unable to complete your request.</p>

<p>Please contact the server administrator at webmaster@localhost to inform them of the time this error occurred, and the actions you performed just before this error.</p>

<p>More information about this error may be available in the server error log.
Apache/2.4.25 (Debian) Server at localhost Port 80</p>
