Sorry, I'm intentionally very ignorant about MTP and Calibre.
It could be that you're missing a directory/permission where it's trying to store something.
You might be able to get more info if you run an "adb logcat" on the Page while syncing.
There are lots of Calibre pros around here though.
See:
https://www.mobileread.com/forums/sh...45&postcount=3