Pascal Zotto

If the app doesn't repair it then it may be too far gone.  You could try something like sqldatabase recovery from here - https://www.sysinfotools.com/ 

No guarantees but I have managed to do some recovery in the past combining this with a lot of work in a text editor and eventually rebuilding the TM.

As the file seems to be completely broken, I managed to get it done another way:

I had a backup of a few months ago (backup task did not work due to some unmonitored error Oo) so I used TextCrawler to search all files in trados projects folder containing for the source and target language string (source-language="fr-FR" target-language="lb-LU">) and then ordered results by date. I then selected the files starting the last updated date, used the option "copy" to copy all the selected files to a specific folder which I them imported that folder into the working TM file.

But thanks for the help.