Error with Racket 5.1.2 and bzlib

[anonymous]

This is the beginning of my program:

#lang racket

(require net/url

net/mime
(lib "match.ss")
(planet neil/htmlprag:1:6)
(planet bzlib/http/client)
(planet lizorkin/sxml:2:1/sxml)
(planet jaymccarthy/ sqlite:4:5/sqlite))

and this is the error message I get when I try to start the program under Racket 5.1.2:

...\AppData?\Roaming\Racket\planet\300\5.1.2\cache\bzlib\base.plt\1\6\base.ss:29:9: module: identifier already imported from a different source in:

identity
scheme/function
mzlib/etc

This problem does not occur with Racket 5.1.1.