Migration and Registration

I tried the migration tool from RHN classic to Subscription management on a RHEL6 system. Everything worked well, unregistered from RHN, went to register on RHSM, and failed. The failure after username and password prompts was:

[Errno 10] No child process

If I try to use the subscription-manager register process, I get the same error. I have verified my username and password with RHN.

Any ideas on how to register this system with RHSM? The website shows that the system is not registered.