Q: "iTunes could not back up the iPhone becuase the backup session failed"

Hello CMC507,

Welcome to the Apple Support Communities!

I understand that you cannot back up or sync your iPhone because iTunes keeps giving you an error. The attached article has steps for troubleshooting the error “… the back up session failed”. Please read over and work through the steps to help resolve this issue. 

If you can't back up or restore your iPhone, iPad, or iPod using iTunes - Apple Support

Cheers,

Joe