The diagnostic suggestions for troubleshooting ejabberd have been exhausted, but still no joy. The symptom is that running olpc-netstatus shows that the XO is doing presence via salut. The strange thing is that ejabberd appears to have seen users, that cannot then connect. Following the instructions at http://wiki.laptop.org/go/XS_Techniques_and_Configuration#Troubleshooting:
# List who is registered with ejabberd # (this happens on the first reboot after the user has used the 'register' option) ejabberdctl registered-users `hostname -f`
The identities of the XO’s that cannot then use ejabberd.