renaming mailbox problems

[Joe Ellis]

imap> renm user/robert~mflexample-com user/rob
renamemailbox: Operation is not supported on mailbox

imap> lam user/robert~mflexample-com
robert~mflexample-com lrswipcda
mailadmin lrswipcda

im using cyrus-imapd-2.0.15-HIERSEP-r2.  i get the same error on
cyrus-imapd-2.0.14 except the '/' is a '.'

any ideas ?

-- 
Joe Ellis