From boston.com:Mike Lowell's agents and Theo Epstein could not reach an agreement about an hour before the midnight deadline in which the Red Sox had exclusive rights to negotiate with Lowell.
Lowell will now be a complete free-agent and can negotiate with other teams.
Both sides agreed there's still room for an agreement to be reached and they'll continue to stay in touch. Lowell will now be able to determine whether there's a four-year market out there for his services. Indications are that the Sox would not move off three years.