Malicious users can cause GW errors - eg
/2 E#myguild##blahblah

Date: 2015-12-28 21:58:19
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\GreenWall\Lib\Base64BCA.lua line 154:
Invalid input, expected type string but got: nil as a: nil
Debug:

GreenWall\Lib\Base64BCA.lua:154: decode()
GreenWall\Channel.lua:410: al_decode()
GreenWall\Channel.lua:390: receive()
GreenWall\GreenWall.lua:366: GreenWall_OnEvent()

  [string "*:OnEvent"]:1

Locals:
(_temporary) = false
(_temporary) = "Invalid input, expected type string but got: nil as a: nil"

Good catch!