Why does the migration fail when permissions are selected for migration?

Answer:

We don't support migration of permissions when the Source or the Destination is SharePoint 2010.

Permission migration will fail if the Source or the Destination is SharePoint 2010, because SharePoint 2013 SDK doesn't provide full functions toward SharePoint 2010. To protect your data from being accessed by unauthorized users, we simply stopped this migration.

To continue, go to Migration Options, remove the checkmark from Permissions, then start the migration again.​