This error means that the user you have connected the migration with does not have access to edit the field named. Please review the permission set/profile of the user and ensure there is access to read/write fields. We also recommend to check the settings on the field itself to ensure it is also set to be able to be edited.
Unable to create/update fields: "x". Please check the security settings of this field and verify that it is read/write for your profile or permission set.
Written by Ashley Milne