Hey sutter,
I documented the way I got it to work, however for most cases the official documentation should be sufficient. https://letsencrypt.org/howitworks/
As to this problem, I haven’t seen it myself, I just tried a dry run, and that worked… Only thing I can think of : is everything up-to-date ? yum update -y
If both methods don’t work you could try other clients, I have recently tried another one called letsencrypt.sh , but there are plenty see List of Client Implementations