New issue 815: Tipsy: Plots fail if index, etc. aren't called first https://bitbucket.org/yt_analysis/yt/issue/815/tipsy-plots-fail-if-index-etc... Ben Keller: SlicePlot and ProjectionPlot will fail unless the smoothed fields are setup (I think?). So if field_list or index, etc. are called before the plot routine. If they aren't the plot fails with an indexError thrown. I think this should be a quick fix...