Error running bismark_genome_preparation

[chrismahony]

I am running:

bismark_genome_preparation --path_to_aligner /my_path/bowtie2-2.5.0-mingw-x86_64/bowtie2-2.5.0-mingw-x86_64/ --verbose /my_path/RRBS/

And I get the following output just after step III launches:

bowtie2-build-s does not exist, try running `[g]make bowtie2-build-s' Parent process: Failed to build index

Could you help?

Thanks Chris