I too am experiencing a problem with accessing Transmission outside my network. I CAN access it with my external ip address, as well as the dyndns.org account I set up. ONLY if i have the ip address from the computer I'm using included in my settings.json file.
I followed the link below and it didn't include the blocklist parameters.
You should take a look at the manpage for transmission-daemon. Here are the relevant portions of the manpage (http://linux.die.net/man/1/transmission-daemon) that deal with that information.