I think I got it...
1 - The file folder names CANNOT contain special characters
The system won't recognize it and you get a failure message
2 - I tried to reconvert 2 DOC files (60,000 words) into DOCX and it works perfectly, allthough it takes some minutes until it is ready for translation.
One other point is: when converting the DOC into DOCX, you'll need to mark the option
"Maintain compatibility with previous Word version"
Following this same logic, the name of the file CANNOT contain special characters, and PERHAPS are empty spaces also not allowed...
And now it's time to go work!