Unable to delete custom statuses

Over the years we’ve created custom statuses in Edit Flow publishing workflow. Some have never been used so we’re trying to clear out those statuses that we will no longer use. When I click the Delete link under a custom status I get a message that says “This site says… Are you sure you want to delete the post status? All posts with this status will be assigned to the default status.” Then I click OK and get a page that says “Are you sure you want to do this?” and a link that says “Please try again”. When I click the link I’m taken back to the Custom Statuses page in Edit Flow but the status I just tried to delete is still there! What’s causing this and how to I fix it?

Thanks!