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.