Using multiple timers and avoiding conflicts
The problem is the Servo library. This library is claiming all the timers, so you can't use them yourself. What I do to fix this is edit the Servo.h (or ServoTimers.h) file. 

#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
//#define _useTimer5
#define _useTimer1
#define _useTimer3
//#define _useTimer4
//typedef enum { _timer5, _timer1, _timer3, _timer4, _Nbr_16timers }   timer16_Sequence_t;
typedef enum { _timer1, _timer3, _Nbr_16timers } timer16_Sequence_t;


This will remove the 2 timers (4 and 5) for the Mega boards, but you can still attach 24 servo's. If you need more, you should edit this file again.