Get xml file to find and replace text. PHP

I need to change texts in a XML file using PHP code. Then I created a code to:

1- get the file

2- replace the texts

3- save the file with other name.

Problem is that I am having some issues to replace some text in a xml file.

I am able to replace simples strings but I can not replace text with characters like '<'. Below the real code and files.

Original XML path: http://www.csainmobiliaria.com/imagenes/fotos/pisos-NOK.xml

1) This code just changes the text Inmuebles to xxxxxxxx. This works fine

    $xml_external_path = 'http://www.csainmobiliaria.com/imagenes/fotos/pisos-NOK.xml';
$xml = file_get_contents($xml_external_path);

$response = strtr($xml, array(
    'Inmuebles' => 'xxxxxxxx'
));

$newXml = $response;

$newXml = simplexml_load_string( $newXml );
$newXml->asXml('/home/csainmobiliaria/www/pisos-NEW.xml');

2) Now, if I use this code to change the text <Table Name="Inmuebles"> to <xxxxxxxx> I get a ERROR 500.

    $xml_external_path = 'http://www.csainmobiliaria.com/imagenes/fotos/pisos-NOK.xml';
$xml = file_get_contents($xml_external_path);

$response = strtr($xml, array(
    '<Table Name="Inmuebles">' => '<xxxxxxxx>'
));

$newXml = $response;

$newXml = simplexml_load_string( $newXml );
$newXml->asXml('/home/csainmobiliaria/www/pisos-NEW.xml');

3) In the same way, if I use this code to remove the text Publicacion I get a ERROR 500.

    $xml_external_path = 'http://www.csainmobiliaria.com/imagenes/fotos/pisos-NOK.xml';
$xml = file_get_contents($xml_external_path);

$response = strtr($xml, array(
    '<Publicacion>' => ''
));

$newXml = $response;

$newXml = simplexml_load_string( $newXml );
$newXml->asXml('/home/csainmobiliaria/www/pisos-NEW.xml');

This is the final result I need to get:http://www.csainmobiliaria.com/imagenes/fotos/pisos-OK.xml

Capture:

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