Well, I meant Forge or Bukkit or Spigot or MCPC+, for instance. I'm using MCPC+ myself and I'm not seeing an error using the /help command with the latest build, but I suppose it could be an unexpected interaction with some other version of the server, or some other mod... or indeed anything else. Some mods I know that support SMP on Forge servers don't work well on MCPC+ or Bukkit and vice-versa.