Unable to add public folder mailbox

I want to create a public folder so that I can create a shared calendar in my organization (that can be updated by multiple users). When I attempt to create a public folder within EAC I'm told I first need to create a public folder mailbox. On the Public Folder Mailboxes tab it states "Click Add to create a public folder mailbox" - Only problem is, I don't have an Add Button!

I submitted a support request via the portal but was just sent a canned response.

Thanks,

Ben