its because you have very strange characters (which are not allowed for xml) in some tags. try this plugin version, it will display some additional info about xml parsing errors (line number and problem char position in line):
http://www.mediafire.com/file/ekct1t8ss36fp29/mb_TagTools_2016-10-05-3.zip
you will need some powerful text editor (eg. notepad++) to find these problem chars because your backup file is very large. you can delete these strange chars in text editor, then import tags back to mb.
I think it's time for me to stop trying to use the Tag Backup feature of the Advanced Tagging Tools plugin.
Using the updated dll I ran a backup and it created a 60mb file called phred=Baseline.bbl. I opened in in Notepad++ and found lots of characters that look like little rectangles but when copied and pasted into a next text doc show as question marks. I certainly haven't looked at every track, but it appears that this character is in every set of lyrics I've looked at. From what you've said, I'm assuming this is the character that's corrupting the backup file. There's just no way I'm going to edit the lyrics of 15,000+ tracks.
Here's a screenshot of one set of lyrics...
I do have one other question regarding the ASR Presets - I extracted the zip file to my Plugins folder. The result was the four language folders and the ASR Presets folder, along with the png and dll. But after enabling and configuring the plugin, there's now a second ASR Presents folder in my AppData folder. Should there be two? And if not, which one should be deleted?
Thanks for all your help on this. At least the Additional Tagging Tools (still) work fine for me.