To test, I changed the applet to try to open /dev/moxer instead of /dev/mixer so that it wouldn't be found. That reproduced the failure.
To fix it, I switched the g_error message to a g_warning in the volume applet and it no longer causes the abort. I have no idea why calling g_error makes hildon-desktop abort but there it is. It's fixed in 0.23.
To test, I changed the applet to try to open /dev/moxer instead of /dev/mixer so that it wouldn't be found. That reproduced the failure.
To fix it, I switched the g_error message to a g_warning in the volume applet and it no longer causes the abort. I have no idea why calling g_error makes hildon-desktop abort but there it is. It's fixed in 0.23.