(This patch applies to version 1.9.8 of GreenWall. If you have already updated GreenWall to version 1.9.9, this patch is no longer necessary, and may in fact cause you to transmit messages in doublevision.)
GreenWall (and a lot of other guild chat addons) broke recently when the guild message format changed from plaintext to a "|K" escape code, which can't be resent through other communications channels. This plugin hooks into your chat editbox to capture your message while it's still in plaintext, rather than waiting for an echo from the server. It also deactivates GW's guild message handler which was causing a Lua error.