SS is Stale Shares discarded (work completed but not submitted because already stale - just as bad as rejected)
When merged mining this is a bad idea. The proof of work may not be valid on the bitcoin chain, but it could still be valid on the namecoin chain. One might potentially throw away a proof of work that would have been able to create a namecoin block.
By the way, it is now possible to enter an NMC cash out address on the website and collect your namecoins. More website updates coming soon.
Some of us have pointed this out and the author is working on an updated version of cgminer which doesn't assume blocks are stale unless it receives an LP.
Right now there is a command line option which will force cgminer to submit all completed shares regardless of it if thinks they are stale. Of course that puts more work load on the server. Hopefully the next version of cgminer will strike a better balance.