You could always use the online galaxy version. Also, can you really trust the results you get from PICRUSt? You have a relatively short stretch of 16S rRNA that is e.g. 98% similar to the 16S rRNA of some reference genome. Based on this, the genome your 16S rRNA represents encodes the same functions as the reference genome? I don't think so. 16S rRNA genes drift apart far, far slower than the protein-coding gene contents of genomes. It might be somewhat decent strategy in like 20 years when we have a much more comprehensive set of reference genomes..
it says: 2.1.5 version ....
Perhaps that function was removed/renamed. Google could maybe tell.
edit. https://groups.google.com/forum/#!topic/picrust-users/WzgQWDVYh9w