auth.log:Nov 28 13:51:43 localhost sshd[19988]: rexec line 12: Deprecated option RhostsAuthentication
Despite the fact that this is one of the most uninformative bugs ever (^_^), it does indeed look like a configuration option has changed in sshd_config -- check the openssh.org site for details. Will see about updating this to the new pubkey authentication syntax.
It was not my intention to submit one of the most uninformative bugs ever. I figured that the subject and log snip was pretty explanatory. Sorry - I'll be more verbose next time around. Anyway, thanks for looking into this.
Fixed in CVS.