We're short on information to actually determine what's wrong here. It looks like you're still using pdb, but I see different output/problem areas from your screenshots. The first one looks like it crashed in tb.start, and the second one looks like it crashed just creating the channel model block. Can you confirm what line is actually crashing, and report your gnuradio + volk version?
If it's at runtime and you're using an older ettus image (rel3? rel2? I haven't kept up with versions and dates) you might be getting bit by this
https://github.com/gnuradio/volk/issues/25 which can be fixed by either adding some lines to volk_config or by upgrading to that latest release.