Failed to upgrade to OS X High Sierra with two non-descriptive errors
I had the same problem with an iMac, 

just delete the update program from your mac and re download it from the App Store. 

If that won't work you should make a Backup with Timemachine and reset your Mac. Try to update again. if it works, recover your data from the backup.

Check this link if you need help with the reset of your system.
https://support.apple.com/kb/PH25649?locale=de_DE&amp;viewlocale=de_DE