Can't say it's exactly that but your loopback0 interface is not part of the 3G VRF and you're sourcing this tunnel from it.
Similarly dialer0 is source of tunnel interface but it's global VRF.
I'm wondering what you're trying to achieve exactly, but when you say "tunnel vrf X" it implies front VRF will be X. I.e. reachability to other hosts (via transport) should be via VRF X.
My suggestion, get this thing going in global VRF, it's pretty easy to add VRF on top.
