This might be completely way off, but it might have something to do with the increased friend count on ps3. As many know you can add 2000 now BUT only 100 APPEAR. Maybe the person inviting you isn't appearing on your friends list at that time.
This was not the case for me. All the friends that I was inviting and that were inviting me, were showing on the XMB and the in-game friends list.
It only broke for me on Sunday afternoon. I played late Saturday night and they were working fine then.
ND may not even be reading the forums anymore! We will forever be stuck with no invites and super nerfed mega bomb
I'll give them a few days.
I'll message macgruber if we don't hear anything within the next few days. if I hear nothing there i'll try eric.
I kind of expect a response first time though he seems pretty reliable.