Apache Shiro keeps redirecting to login page

I am having some troubles with Apache Shiro when I put the right user and password in the login page. It keeps redirecting me to the same page every time.

Here I have my project structure.

Now my Shiro ini file content

[main]
# specify login page
authc.loginUrl = /admin/login.jsp
authc.successUrl  = /admin/administracion.jsp

[users]
admin  = admin
guest = 12345

[urls]
/admin/login.jsp = authc
/admin/** = authc

Now, the login html form

<form class="formulario" name="loginform" action="" method="POST">
                <div id="descripcionPagina">
                    <h1>Login</h1><br>
                    Para ingresar al sistema <font color="red">identifíquese</font> como usuario del sistema.
                    <br>
                </div>
                <table id="tabla3" width="65%" cellpadding="8">
                    <tr id="fila">
                        <td align="right">
                            Identificación:&nbsp;
                        </td><td>
                            <input type="text" size="30"
                                   id="Lusuario" name="user">
                        </td>
                    </tr><tr id="fila">
                        <td align="right">
                            Clave:&nbsp;
                        </td><td>
                            <input type="password" size="30"
                                   id="Lpassword" name="password">
                        </td>
                    </tr><tr id="fila">
                        <td align="center" colspan="2">
                            <input type="submit" value="Ingresar">
                        </td>
                    </tr>
                </table>
            </form>

The web.xml is fine and doesn't contain any web session parameters. Any help would be very appreciated. Thank you.