Problems with LuaPlus::LuaState::RegisterDirect function

I am having problems with the LuaPlus::LuaState function RegisterDirect. This function will allow for user defined functions to be registered without the LuaState as a parameter. You can pass in any function with any parameters and return values. The problem I have is that this function throws a System.TypeLoadException in VS .net 2003. It says that the lua_state type could not be loaded. I have initialized the LuaState that I am using and I have tried both using LuaState and LuaState Owner. Any ideas?? Let me know if you wanna see any code?