importing XLIFF file after translation is failing

I have followed the instructions for translating my course, e.g. created a duplicate then exported it as an XLIFF and emailed it to the translator. An initial test with just a few lines translated worked perfectly. The language I need is Ukrainian.

The translator has been trying different XLIFF software/apps but each time I have tested to see if it will import it shows it is uploading, then processing then it says 'Import failed". 

I have just tried again, importing the translation using the original software which was successful, and that too is failing to import now.

I urgently need yo resolve this as the course is a pre-read for a workshop I am running virtually on 28th October and it still needs translating.

Is there any particular XLIFF software/app that works well with Rise 360?

Please help.