Trackster complains to me when I try to load up my custom reference genome to compare some sample data to.

"could not load chroms for this dbkey"

I think it's because I'm using the newest g1k human ref genome v37, and I don't know if the hg19.len file works with it...

I generated my own twobit file for it, but now I think I need the .len file...

To be honest I'm kind of lost. Where does trackster even look for my genome, and how do I generate a .len file?
(I read the visualizations page and the custom genome docs page)