This error probably means there is some small data input issue to resolved. There are a few ways to narrow it down.
First, try this with a smaller group of sample of data, maybe 3 samples, same result or does something different happen?
From there, you can compare to the tutorial example linked at the bottom of the tool form. Does the example work for you? Does the protocol differ from what you are doing? Do you notice anything relevant about the file formats?
These tutorial were just recently updated, and there are two versions, one longer and detailed and the other short. These also include workflow templates.
Galaxy Training! tutorials for HUMAnN: to profile presence/absence and abundance of microbial pathways and gene families
Please give that a try and let us know what happens! If the smaller set of samples also fails, you are welcome to share that back here for help working out what to troubleshoot next! Screenshots are sometimes enough but a shared history link is best and fastest!
Let’s start there, thanks! 