Hi Mariana Alcantara 
The information you provide may not be sufficient to give much of an answer. A printout of the stack trace is helpful for the more technically minded here on this forum.
I am trying to figure out the whole story... You received an XLIFF file? Why not finalize your project the normal way?
Wonderment: Would merging and splitting segments cause this kind of problem?
Daniel

Hi Mariana Alcantara

The .xlf file ending is for XLIFF files. An XLF file is an XLIFF file. So if you received a file like translate_me.xlf, you received an XLIFF file. (Check it out on Wikipedia to get a first impression:https://en.wikipedia.org/wiki/XLIFF) The first line of your source file should say something like this if you open it with Notepad:

<xliff version="1.2">

You can import an XLIFF or XLF file with Studio no problem as it is THE file standard for localization.

Studio will convert this file to its own format, which is called SDLXLIFF, an XLIFF variant which contains additional information Studio needs.

MemoQ may or may not be able to process SDLXLIFF files, but it surely is able to process XLIFF files. So if you get an XLF file, translate it and click "Finalize", Studio will generate an XLIFF file. (Check the first line of the target file with Notepad, it should start with "<xliff ...." and end with ">". Could you post just that one line here on the forum?

How to get the stack trace:

Daniel