Hi @kzpx67,
If you haven’t checked it out already this webpage we have a lot of details on the tuning process and how it works. Its likely that your low sample numbers are what is causing the error during tuning. An alternative approach is to simply extract the loadings of your features and use that to identify your important discriminating features (see this post).
When you run tune() on a mint.splsda object, it will internally run tune.mint.splsda(), so you can use either function they are the same.
Cheers,
Eva