I'm having the same issue.  I'm mining Callisto (CLO).  I had been using Parity with its built-in stratum support, but since they have not updated their Parity client (rust-callisto) for last week's hard fork, I tried to switch to Geth, which doesn't have stratum - thus needing to switch to the RPC interface for get_work.  This is where the issue comes in.

I am setting the coin on the commandline.

I tried setting a "password' in commandline as suggested above, but that doesn't make a difference.  Over the past few days, I've also tried as many other options as I can.  It appears that the issue is it's connecting on RPC for get_work, but there's still a watchdog for a Stratum thread - but since we're not using Stratum, it sees no activity and bombs out.

See here - you can see that the coin is properly set, has connected to geth successfully, and has started mining, but at 51s, it kills itself because of the stratum thread.