Thread.py error snakemake

Estoy tratando de ejecutar un archivo simple de serpiente de una regla de la siguiente manera:

resources_dir='resources'

rule downloadReference:
    output:
        fa = resources_dir+'/human_g1k_v37.fasta',
        fai = resources_dir+'/human_g1k_v37.fasta.fai',
    shell:
        ('mkdir -p '+resources_dir+'; cd '+resources_dir+'; ' +
        'wget ftp://ftp-trace.ncbi.nih.gov/1000genomes/ftp/technical/reference/human_g1k_v37.fasta.gz; gunzip human_g1k_v37.fasta.gz; ' +
        'wget ftp://ftp-trace.ncbi.nih.gov/1000genomes/ftp/technical/reference/human_g1k_v37.fasta.fai;')

Pero me sale un error como:

    Error in job downloadReference while creating output files 
    resources/human_g1k_v37.fasta, resources/human_g1k_v37.fasta.fai.
    RuleException:
    CalledProcessError in line 10 of 
    /lustre4/home/masih/projects/NGS_pipeline/snake_test:
    Command 'mkdir -p resources; cd resources; wget ftp://ftp-
  trace.ncbi.nih.gov/1000genomes/ftp/technical/reference/human_g1k_v37.fasta.gz; gunzip human_g1k_v37.fasta.gz; wget ftp://ftp-trace.ncbi.nih.gov/1000genomes/ftp/technical/reference/human_g1k_v37.fasta.fai;' returned non-zero exit status 2.
      File "/lustre4/home/masih/projects/NGS_pipeline/snake_test", line 10, in __rule_downloadReference
      File "/home/masih/miniconda3/lib/python3.6/concurrent/futures/thread.py", line 55, in run
    Removing output files of failed job downloadReference since they might be corrupted:
    resources/human_g1k_v37.fasta
    Will exit after finishing currently running jobs.
    Exiting because a job execution failed. Look above for error message

No estoy usando la opción de hilos en snakemake. No puedo entender cómo se relaciona esto con thread.py. ¿Alguien tiene experiencia con este error?