problems with splitting and imap

[Richard Riley]

A couple of days ago I had to remove all my splitting code because of
this error:

,----
| Debugger entered--Lisp error: (wrong-type-argument listp "(Unparsable address 
-- Strange character \\> found: \">_^_\")")
|   bbdb/gnus-split-method()
|   nnimap-split-to-groups(bbdb/gnus-split-method)
|   nnimap-split-articles(nil "mymail")
|   nnimap-request-scan(nil "mymail")
|   gnus-request-scan(nil (nnimap "mymail" (nnimap-stream ssl) (nnimap-address 
"imap.richardriley.net") (nnimap-authinfo-file "~/.authinfo") 
(nnir-search-engine imap)))
|   gnus-read-active-file-1((nnimap "mymail" (nnimap-stream ssl) 
(nnimap-address "imap.richardriley.net") (nnimap-authinfo-file "~/.authinfo") 
(nnir-search-engine imap)) nil)
|   gnus-read-active-file()
|   gnus-group-get-new-news(nil)
|   gnus-1(nil nil nil)
|   gnus(nil)
|   call-interactively(gnus nil nil)
`----

Could someone please suggest how to fix this/locate the offending message?

I'm talking to a dovecot IMAP server btw.