IMAP "Trying to require method that doesn't exist"

[J Kenneth King]

This is the relevant part of my .gnus.el:

(setq gnus-secondary-select-methods
      '((nnimap "mail.digisphereinc.com"
                (nnimap-address "mail.digisphereinc.com")
                (nnimap-list-pattern "INBOX")
                (nnimap-authinfo-file "~/.authinfo")
                (nnimap-stream ssl))))

I then use .authinfo to store all of my passwords, etc It appears to
connect to the server fine, but when I press RET from the Group buffer,
I just get the response "Trying to require method that doesn't exist."

Any ideas what I'm doing wrong?

Cheers