Bingo. You need the BB data plan. Am seeing and hearing more and more that the current DM and OS versions for both Windows and Mac require the user to have a BB data plan active. Don't ask why. Ask RIM and your carrier that question.
I thought the latest Mac DM was 1.03, not 4.5 something.
Are you DM for the Mac or are you using the PC version using Bootcamp/Parallels/VMFusion?