i get a slightly different error doing that.
AcmNotPossible calling acmStreamSize
at NAudio.MmException.Try(MmResult result, String function)
at NAudio.Wave.Compression.AcmStream.SourceToDest(Int32 source)
at NAudio.Wave.WaveFormatConversionStream.SourceToDest(Int32 source)
at NAudio.Wave.WaveFormatConversionStream..ctor(WaveFormat targetFormat, WaveStream sourceStream)