enumeration

struct Timer { enum TIMERSTATE eEtat ; unsigned long ulValue ; unsigned long ulTempo ; } ;

why i'd got an error that say : error: field 'eEtat' has incomplete type

you must define the enum outside/before the struct like below

enum TIMERSTATE {A, B };

struct Timer {
   TIMERSTATE eEtat ;
   unsigned long ulValue ;
   unsigned long ulTempo ;
} ;

void setup(){}
void loop(){}