Please note that the errors Fluxa gives when not able to load samples don't always accurately reflect the nature of the issue. There is some oddness there and I seem to remember the source and comments reflected that when I last looked into loading samples. Back then the issue was a non-standard header which I don't believe can be the issue now.
it seems to be a bug. i got this:
async loading: sample.wav Error opening [sample.wav] async loading: /opt/local/share/fluxus-017/material/samples/sample.wav
