The command lines I used is:
time qiime feature-classifier classify-sklearn
--i-classifier 12S-seqs.qza
--i-reads rep-seqs.qza
--o-classification silvataxonomy.qza
And the error message is: There was a problem with the command:
(1/1) Invalid value for '--i-classifier': Expected an artifact of at least type TaxonomicClassifier. An artifact of type FeatureData[Sequence] was provided.
As it mentions in the error, this command needs a TaxonomicClassifier instead of sequences.
Are you trying to use a custom 12S database to classify your reads? If so, you might want to check out the RESCRIPt plugin or this post about building a 12S database with RESCRIPt.