The e-mail could not be sent.
Possible reason: your host may have disabled the mail() function...
I've gone through the other forums and can't seem to get this to work. I just set up wpmu for the first time on my local machine (Mac OS 10.4). Most of the forums seem to be about similar problems on windows installs or goddady hosted installs, but the solutions to those installs haven't worked for me.
One thing I did notice in another forum, and which may be the root cause, is that typing this:
mail -s "Testing Email fromhostname" <youremailaddress>
simply hangs and I have to kill it. Does this mean I just need to set up a mail server on my mac? In which case, this guy's probably got me covered -- http://technosailor.com/2006/10/25/how-to-configure-your-mac-to-send-mail-regardless-of-where-you-are/ ? Anything else I should be paying attention to? Forgive me if this is entirely obvious, but I'm still a bit of a newbie.