I am trying to use the Dissolve_management tool using ArcPy. I keep getting an error that reads "Parameters are not valid.", and I cannot figure out where I am going wrong. Here is the code: 

    env.workspace = "H:/Data/"
    input = "Analysis/mtbs_state_2000/al.shp"
    output = "Analysis/2000_dissolved/al.shp"
    statistics_fields = [["km2", "SUM"], ["HU90", "SUM"]]
    arcpy.Dissolve_management(input, output, "Fire_ID", statistics_fields)


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  [1]: https://i.sstatic.net/hT5u1.png