Hi nodnyl, these forums are not designed to be the primary means of contacting NCH support, but are for forum members helping other members. Instead there is a support link on nearly every page of the NCH website including on the landing page for MixPad. To contact the MixPad support team, please visit http://www.nch.com.au/support/supportcontact.html?software=MixPad
After your post on the 16th, I emailed one of the developers and just received his response this morning. He suggested checking on the following:
1. Have you checked the audio options tab and made sure that the correct device is set for playback.
2. Can you play other types of audio files? eg. wav, wma etc.
3. Can you record?
However, as mentioned above, it would be best for you to contact the support team through link I provided.