I have the same problem :
I use the programming code below, but could not make it work :https://www.arduino.cc/en/Tutorial/RobotLineFollowing
The robot runs the program and play music endlessly. If I put in comment the program line to start the music file , the robot calculates the time, turns right and left and then stops without following the line.
I have two robots and I have the same problem. Someone would have an idea?