SSN ontology not classifying with Pellet and Fact++

I am trying to classify the SSN ontology at

http://purl.oclc.org/NET/ssnx/ssn

The Pellet 2.3.1 command line refuses to classify and throws an
out-of-memory error. In Protege, if I load the ontology and classify it
using Hermit, the classification works fine. If I use Pellet or Fact++
through Protege, the ontology fails to classify. Is this a known behaviour ?

I need to import SSN in my ontology and this makes me concerned about doing
so.

Thanks,

Monika