Steve Denning lists ten management objections to Agile software development.
I've found his second objection to be one of the biggest barriers to Agile. "Agile doesn't fit our organizational culture."
Because Agile is self-organizing and projects are managed by three groups — product owner, Scrum team, and Scrum Master, functional managers are no longer needed to manage projects. This creates conflict and is often one of the reasons Agile has a hard time succeeding in an organization.