[galaxy-dev] Bcftools to convert bcf to vcf

I run my own files against my own reference with bowtie. In order to obtain SNPs, I use Mpile to get .bcf file. When I try to use bcftools to convert bcf to vcf. The output is always "tabuler" and size of file always less than 1k. It seems like the system can't process my bcf. Is there any setting I should apply or any setting I should modify? In previous steps, I didn't change any setting. Thank you