I have created a simple xml file type with embedded content processing via html5. I have also specified html content in the Excel bilingual file type. Now I have 3 xml and 1 xlsx file in the project. When I try to open them as virtual merge, I get "Object reference not set...". However, I can open any of these files separately.

The structure of first xml file

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Root>
<articles>
<article>
<ordernumber>SW10002</ordernumber>
<mainnumber>SW10002</mainnumber>
<translation>
<languageId>3</languageId>
<translationname></translationname>
<translatedescriptionLong></translatedescriptionLong>
<translatedescription></translatedescription>
<translation_extras></translation_extras>
<translation_material></translation_material>
<translation_materialproperties></translation_materialproperties>
<translation_usps></translation_usps>
</translation>
<translation>
<languageId>4</languageId>
<translationname></translationname>
<translatedescriptionLong></translatedescriptionLong>
<translatedescription></translatedescription>
<translation_extras></translation_extras>
<translation_material></translation_material>
<translation_materialproperties></translation_materialproperties>
<translation_usps></translation_usps>
</translation>
<translation>
<languageId>5</languageId>
<translationname></translationname>
<translatedescriptionLong></translatedescriptionLong>
<translatedescription></translatedescription>
<translation_extras></translation_extras>
<translation_material></translation_material>
<translation_materialproperties></translation_materialproperties>
<translation_usps></translation_usps>
</translation>
<translation>
<languageId>6</languageId>
<translationname></translationname>
<translatedescriptionLong></translatedescriptionLong>
<translatedescription></translatedescription>
<translation_extras></translation_extras>
<translation_material></translation_material>
<translation_materialproperties></translation_materialproperties>
<translation_usps></translation_usps>
</translation>
</article>

The second xml file

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Root>
<Header>
<HeaderChild></HeaderChild>
</Header>
<Translations>
<Translation>
<objectKey>5</objectKey>
<objectType>configuratorgroup</objectType>
<baseName>Temperaturbereich</baseName>
<name>Temprature Ranges</name>
<description></description>
<languageId>3</languageId>
</Translation>

And the third xml file

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Root>
<Header>
<HeaderChild></HeaderChild>
</Header>
<Translations>
<Translation>
<categoryId>5</categoryId>
<languageId>3</languageId>
<description>Products</description>
<external></external>
<externalTarget></externalTarget>
<imagePath></imagePath>
<cmsheadline>Coolers from QOOL®</cmsheadline>
<cmstext><![CDATA[<p><span>The QOOL</span><span>®</span><span>&nbsp;Box in combination with the QOOL</span><span>®</span><span>&nbsp;Temperature Elements provide innovative premium cooling options – perfect for any Adventure.</span></p>]]></cmstext>
<metatitle></metatitle>
<metadescription></metadescription>
<metakeywords></metakeywords>
</Translation>

The parser rules for my xml filter are:

I cannot open neither all xml files together or any xml file and the Excel together. Opening separatedly works.

Any idea, what can be wrong here?