FYI - I had this issue as well, on a laptop where I am dual-booting Win10 and Ubuntu 16.10. The laptop has been configured with three partitions, one each for Win and Linux, and a third formatted as NTFS for my data. insync running on Ubuntu syncs the folder to the NTFS partition. I use Ubuntu the most, so it gets the sync duties, but when I happen to boot to Win10, I have my data accessible. It will sync the next time I boot to Linux.
This works fine, EXCEPT: When using Win10, you have to configure it to properly shut down. The default setup will use a "fast shutdown" and "fast boot" setup whereby it does a partial hibernate. This will leave your NTFS partition in a "locked" state, and Ubuntu will not mount it read-write on the next boot if this happens. You have to go boot back into Win10, change the setting, and do a proper shutdown.
If this setup sounds similar to something you're doing, do a Google search for the error you had. I'm pretty sure that's where I started when it happened to me.