Client fails to open .xlf file translated with Studio 2015

Question

Hello community, 
 My client is translating their website in about 30 languages and has hired some developers to implement that. Those guys sent us translators an .xlf file. I didn't have any problems while translating the file (some HTML tags appear in the text but that's bearable) and the target file generated without any problem. However when trying to import the file on their platform (they use Drupal, I think), they cannot do it. Here is what they wrote:

WRONG STRUCTURE (XML) Looks like all translation were added but uses another xml structure and file can't be imported. Will be need to correct xml format of import file

It seems that other translators' files, 3 or 4 of them, have the same problem, while other languages import well. It may be due to the CAT tool used, I don't know. The dev guys sent a file for Dutch that has imported successfully. When I open this in Notepad++, here is what I see:

While my translation looks like this:

In my file there are obviously more tags that come from I don't know where: I don't see them in Studio. I tried to move up and down in the file type list different XLIFF file types and create new projects accordingly but the result is the same. The developers insist I send a file with correct xml structure but I don't know how to achieve this. 
 
 Please help.

Evzen Polenka · Accepted Answer

You need to turn on this option in XLIFF file type settings in order to NOT put the "extra" <mrk> tags in the translated file:

Trados Studio > 1. Trados Studio

Client fails to open .xlf file translated with Studio 2015