lua_State * pointers

Hi.I''ve managed to create an engine wich unify all it''s parts through a console wich is using lua to manage the rest.I have some lua threads(lua_State * pointers) in each of the engine parts(renderer, input system, etc) in wich i execute specific commands.my problem is:i want to switch through this pointers so one of it and only one should be active at a given time.so let''s say i have: lua_State * x1; lua_State * x2;//both of them are initialized and are running //command whenever i want //and i have lua_State * current = NULL; What I want is to do operations like current = x1; or current = x2; and to run the commands in the current thread.so the idea is so i can switch between the states.the build of the project runs ok but the problem appears on execution where i get an error: adress "an address in hexa of the specified thread" cannot be "read".so why''s that and how can i assign to my "current" pointer one of the other pointers.Normally it should work cause they have the same type, but it doesn''t.. please help Mihai