各位大神好，我在测序单细胞转录组可变剪切分析软件Outrigger时，在index之后进行validate，但是总是出现错误：

File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/bin/outrigger", line 6, in <module>

    sys.exit(outrigger.commandline.main())

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/outrigger/commandline.py", line 1071, in main

    cl = CommandLine(sys.argv[1:])

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/outrigger/commandline.py", line 344, in __init__

    self.args.func()

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/outrigger/commandline.py", line 352, in validate

    validate.execute()

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/outrigger/commandline.py", line 834, in execute

    exonA, exonB, splice_abbrev)

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/outrigger/commandline.py", line 787, in exon_pair_splice_sites

    exonA, splice_abbrev, 'downstream')

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/outrigger/commandline.py", line 800, in individual_exon_splice_sites

    exon_bed, self.genome, self.fasta, direction)

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/outrigger/validate/check_splice_sites.py", line 57, in read_splice_sites

    flanked = bed.flank(l=left, r=right, s=True, genome=genome)

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/pybedtools/bedtool.py", line 806, in decorated

result = method(self, *args, **kwargs)

  File "/hwfssz1/ST_MCHRI/DISEASE/USER/maoyong/software/anaconda3/envs/outrigger-env/lib/python3.5/site-packages/pybedtools/bedtool.py", line 204, in not_implemented_func

    raise NotImplementedError(help_str)

NotImplementedError: "flankBed" does not appear to be installed or on the path, so this method is disabled.  Please install a more recent version of BEDTools and re-import to use this method.

我是按照给的例子进行操作的，感到十分不解。

请问这是什么原因呢?