The recent update for World of Warcraft, version 5.4.7, introduced a small change that causes older versions of the GreenWall add-on to break. Please update your copy of GreenWall to v1.3.6 to ensure that your messages can be seen by other co-guilds.
GitHub: https://github.com/AIE-Guild/GreenWall/releases/tag/v1.3.6