Servomotor and music shield
Is this the MusicPlayer.h that you have?  https://github.com/Seeed-Studio/Music_Shield

From the description it says:


  The music player reads data from SD card and then feed into the VS1053 chip via SPI bus. This is done in TIMER1's ISR with a interval of 2ms. This job has a high priority and uses the cpu exclusively. In the spare cpu time, player does some process control, like play/pause.


That's the same timer that Servo.h uses.  So the two libraries are not compatible.  You could try using ServoTimer2 library or rewriting this library to get the 2ms timer with Timer 2.