After migrating a SharePoint site or site collection to SharePoint 2013, users with an otherwise valid SharePoint account cannot log into their sites, and are greeted with the error "Sorry, this site hasn't been shared with you."
This is a known issue in SharePoint, (sometimes without even migrating) caused by implementing the incorrect authentication on the target, i.e. NTLM instead of Claims Authentication.
It is often resolved by performing the steps and implementing the script in the following articles:
