[SOLVED] initiation of struct

Another option, as i think was mentioned is to create an initialiser for the struct:

struct Error
{
    byte    code;
    boolean active;
    char    msg[21];
    Error(byte code_, boolean active_, char* msg_) {
      code = code_;
      active = active_;
      strncpy(msg,msg_,21);
    }
};

Error someError = Error(1,false,"some error");

You could use your errorStates struct like this:

struct ErrorStates {
  Error ERR_A;
  Error ERR_B;
};

ErrorStates states = {someError,Error(2,true,"some other error")}; //just an example

But it would be far easier to use if it were just this (without the second struct):

Error errorSates[] =  {Error(1,false,"some error"),Error(2,true,"some other error")};

Then you could do stuff like this:

Serial.print(errorStates[1].msg); //just for example