That's in the constructor again.
Stack trace:
at NAudio.MmException.Try(MmResult result, String function) in D:\\VS Projects\\NAudio 1.5\\NAudio\\Wave\\MmeInterop\\MmException.cs:line 39
at NAudio.Wave.Compression.AcmStream.SourceToDest(Int32 source) in D:\\VS Projects\\NAudio 1.5\\NAudio\\Wave\\Compression\\AcmStream.cs:line 75
at NAudio.Wave.WaveFormatConversionStream.SourceToDest(Int32 source) in D:\\VS Projects\\NAudio 1.5\\NAudio\\Wave\\WaveStreams\\WaveFormatConversionStream.cs:line 55
at NAudio.Wave.WaveFormatConversionStream..ctor(WaveFormat targetFormat, WaveStream sourceStream) in D:\\VS Projects\\NAudio 1.5\\NAudio\\Wave\\WaveStreams\\WaveFormatConversionStream.cs:line 46
at NAudioDemo.AcmPanel.EncodeFile() in D:\\VS Projects\\NAudio 1.5\\NAudioDemo\\AcmDemo\\AcmPanel.cs:line 126
at NAudioDemo.AcmPanel.buttonEncode_Click(Object sender, EventArgs args) in D:\\VS Projects\\NAudio 1.5\\NAudioDemo\\AcmDemo\\AcmPanel.cs:line 33"