Some people asked me this question for a few times, some even mistook it as Fidelizer error so allow me to elaborate why this happens.

Using foobar2000 + wasapi is optional recommendation for bit-perfect playback. I believe you may also need to learn about bit-perfect playback and exclusive access for why error happens. Using WASAPI exclusive will need to have audio output locked to specific application, in this case it’s foobar. If you have other processes occupying audio output like playing YouTube or having other software using audio, it won’t work.

Please keep in mind that using bit-perfect playback will require audio device to support source format. You may need downsampling to play hires tracks using bit-perfect output for audio devices that doesn’t support. You can change to DirectSound so it won’t require to acquire exclusive access though sound will come through system mixer with default sampling rate applied. Anyway, it’s error without foobar playback by itself and has nothing to do with Fidelizer. You can still use Fidelizer effectively with VLC and others.

I hope this will clear out the confusion about bit-perfect playback in foobar2000 software I suggested.