Please share the subscription-manager command you are using to register the system as well as the exact output (error message) of that command. No idea why you cannot upload the log (never used the forums upload feature), but maybe you are able to share the relevant timeframe from /var/log/foreman/production.log either via inline paste or via a pastebin service?
Just to rule the first possible error out: have you installed the katello-consumer package on the workstation? It is usually acessible via http://foreman.example.com/pub/katello-ca-consumer-latest.noarch.rpm for RPM based distros or as bash script via https://foreman.example.com/pub/katello-rhsm-consumer as a more distibution-independant solution. That installs the relevant certificates for the communication between host and Foreman. Without those, the SSL connection will not work.