This is my first foray into doing halo finding / merger tree analysis so forgive me if I'm just missing something simple. My goal is to be able to identify a halo at lower-z that had specific properties at higher-z so I can get its lagrangian volume at lower-z to build a nested zoom. (And I'm assuming merger trees are the only / best way to identify the halo across snapshots for this).

Anyway, I've been following the docs for yt_astro_analysis to build halo catalogs for a series of datasets and just tried the example in treefarm to build a merger tree, but I get an error. I'm using the last_yt3 changeset of yt, am on the master branch of treefarm, and halos were generated using rockstar-galaxies via master branch of yt_astro_analysis. And the datasets are DM-only Enzo runs.

I get this error: http://paste.yt-project.org/show/256/

When running this (slightly modified from the example code): 

Thanks for the help!!

Best,

Andrew