Maybe the BOff thing isn't done anymore. They used to act as regular inventory for the most part. I have had them in my inventory after buying them on the exchange, recieving them in mail, and so on. That was a while ago, though. They still do, really.
And I cleared space on my DOff roster and I still couldn't accept. It's done this to me before. It just eventually let me take it without me having to change my DOff roster. So I still think it's a bug.
Actually they are I have done them recently. The difference is youy are getting individual DOffs, which go straight to your raoster, as opposed to the cadre pack which goes into your inventry with the pic of three faces. Given the pics are you sure you cleared spacin in the DOffs and not BOff spaces.