For reasons that aren't completely clear at the moment, the impact parameter calculation we usually use for b-tagging sometimes fails. The result is that we enter nonsense values, which DIPS consumes, which then become NAN in the DIPS outputs, which throws an error in DL1d.
I'm fixing this by adding a flag on tracks that have an invalid IP, which then signals DIPS to pass through an isDefaults flag so that DL1d can set defaults on the DIPS inputs.