A user reported they could not use RWW or the RDP gateway to connect to their PC at the office. Oddly enough, they were able to connect to another machine - just not theirs. Internally, we were able to RDP into the machine so we knew it was not a problem with the machine itself.
After some research, we found this article on the Official SBS blog and got the answer. The PC was a new unit and we named it using a machine name that was used for an older machine. When SBS adds a machine into the domain, it creates an A record in the internal DNS. When you remove the machine from the domain, that record is not deleted.
So, we updated the A record with the IP for the new machine and we were good to go!