Error running LefSe

Hello! I’m having some problems running LefSe. When running the command:

lefse(shared=R_outputs/shared.tsv, design=R_outputs/design.tsv), I get the following error:

You did not provide a class, using Type.
Comparing Saline_Lake-Freshwater:
[ERROR]: requesting groups not present in files, aborting.
Segmentation fault: 11

Could you please help?
Thanks in advance!!