Thanks for the quick response, Jay. I've tried several different settings:
My machine has 16GB ram, so I didn't keep reducing the size. Everytime I reduced the sort-buffer-size setting it would take longer to use up all the ram, but it still did eventually and then would give the Communication Failure error.
Since the work was slightly time-sensitive, I uninstalled GL version 1.3 and reinstalled version 1.1 and things are working again.
I don't think I can recreate a working example, since the SFrame it's sorting is quite large, but I can give you some ideas to recreate the error on your own. I'm sorting a 2.5GB file of addresses by Zip Code. I know that the sort is lazy, so after the sort, the code has a call 'SFrame.addrownumber()' which would force the sort and add an index. It's here when it hangs.
Let me know if you need more information!