createmailbox: Invalid mailbox name

[Chris Harms]

So I've hit a wall in attempting to move our mailboxes onto a new 
server.  I've built/installed Simon's RPMs for 2.3.8 on x86_64.
After tarring up my old mail spool (2.2.12 on x86) and dumping the 
mailboxes file to a flat format and copying to the new machine, I am 
unable to reconstruct any mailboxes.  It merely exits silently. 

I can create mailboxes in the default domain (cm user/test), but if I 
attempt to create virtual domain users e.g.
cm user/test at domain.tld
I get
"createmailbox: Invalid mailbox name"

What am I doing wrong?

Thanks,
Chris

# imapd.conf entries
configdirectory: /var/lib/imap
defaultpartition: default
partition-default: /var/spool/imap
fulldirhash: 0
hashimapspool: 1
duplicate_db: skiplist
mboxlist_db: skiplist
admins: cyrus at mail
sasl_pwcheck_method: auxprop
virtdomains: userid
defaultdomain: mail #(this is not the machine's name)
unixhierarchysep: on
tls_cert_file: /etc/pki/cyrus-imapd/cyrus-imapd.pem
tls_key_file: /etc/pki/cyrus-imapd/cyrus-imapd.pem
tls_ca_file: /etc/pki/tls/certs/ca-bundle.crt
allownanonymouslogin: no
allowplaintext: yes
allowusermoves: yes
loginrealms: mail domain1.tld domain2.tld