Error messages--Not all text was translated and Unsupported Xliff file: Invalid Character in...

We received a couple of XLF files from a client to translated into a couple of languages.  The translators all use Trados to translate files.  Recently the client said some of the files they received did not import and some did.  All used the same Storyline XLF file to translated.

Articulate is not very efficient in giving what an error might be in a file.  The attached image is typically what client sends back when there is an upload issue. How do you find out what caused this issue?  Typically cannot spend weeks trying to find what might be issue in file or have translator re-translate in hopes that might solve whatever the problem is.

I did get from client a little more info about possible error for French translation.  "Not all text was translated to French. Just the first 5 slides in this module".  However, when I open the file it is had two segments that were not translated.  Why would this keep the file from importing?  What if the EN word just happens to be the same in that language (i.e. croissant)?

I did find something in the Community site: "Initially, the state for each caption in an XLIFF file is "new." When a caption is translated, your translation tool should update the state to "translated.""

I went through the one file that has the "Not all text" and found where it did not have "translated" in WordPad.  I saved the file and now getting this error message: "Unsupported XLIFF file: Invalid character in the given encoding. Line 1, position 718"

It was just a basic save in word pad. Should not cause an issue, unless this invalid character ended up being but in there by my accidentally.  So, how would I find this Line 1, position 718?