hm, one reason on that page could be that artsd or another sound
daemon is running, so beast can't open /dev/dsp until that daemon
has been stopped.
but since you say you don't have artsd running (beware sound daemons
may be started in the background automatically), and since no beast
version is mentioned here, the only clue provided is:
> beast:BSE-Error:3: Failed to open PCM devices: Device not async capable
and that'll only occour if the following code during /dev/dsp initialization
failed to execute:
/* to get usable low-latency behaviour with OSS, we
* make the device blocking, choose small fragments
* and read() the first fragment once available.
d_long = fcntl (fd, F_GETFL);
d_long &= ~O_NONBLOCK;
if (fcntl (fd, F_SETFL, d_long))
i.e. the device can't be set to non-blocking io for whatever reason.
usually that means that the OSS driver is buggy and has to be fixed
in the kernel.