what this error mean ("Failed to open recording device! SDL Error: Too many open audio devices")

when I try to run this program I get the error ("Failed to open recording device! SDL Error: Too many open audio devices") why?

this is my program:

SDL_AudioSpec wav_spec;

  Uint32 wav_length;

  Uint8 *wav_buffer;

  SDL_AudioSpec desired;

  SDL_AudioSpec obtained;

  SDL_zero(desired);

  desired.freq = 44100;

  desired.format = AUDIO_S8;

  desired.channels = 2;

  desired.samples = 4096;

  desired.callback = NULL;

  //Default audio spec

  SDL_AudioSpec desiredRecordingSpec;

  SDL_zero(desiredRecordingSpec);

  desiredRecordingSpec.freq = 44100;

  desiredRecordingSpec.format = AUDIO_F32;

  desiredRecordingSpec.channels = 2;

  desiredRecordingSpec.samples = 4096;

  desiredRecordingSpec.callback = audioRecordingCallback;

  …