Hi Laura!
I think you might be experiencing the same problems I had when I first started experimenting with Moodle 'Books'!
If I remember correctly, the mthml format is the single file web-page format and I found it doesn't work!
You need to save in htm/html format where you obtain a html file and a folder that contains images of the page. Both need to be uploaded to the Moodle course files - easiest way is to put both into a folder, zip it into a single file,
upload the zip file to the Moodle course files, unzip it. Then when you import into your 'Book' you just choose the htm file you uploaded.
Hope this makes sense and works - cheers,
Tony
