Hi @mustilife,
The good news is that it isn't a problem on your end 
The bad news is that you'll have to wait a short time before you can issue your certificate with that tool. Apologies,
SSL For Free (and other web-based ACME clients) is broken right now due to a regression that we're in the process of fixing.
The problem should be resolved in ~30-60 minutes. Please follow this thread for more information.