Hello there,
I have downloaded Forge 10.13.0.1179 for Minecraft 1.7.10 (the latest beta release at time of writing) and when attempting to join my friends realm the game closes, and the launcher re-appears and displays a crash report. I have not added any mods other than the ones downloaded from the Forge website, and I have used the installer to set up a forge profile. I have searched around the forge forums and on google and I cannot find anyone reporting a realms error for MC1.7.10.
Here is a link to the fml-client-latest.log for the error:
http://pastebin.com/hyGqp7Vn