[plt-scheme] bug installing PLAI language in 4.1.5?

Hi,

I've just downloaded the latest version of DrScheme and tried to  
install the PLAI package (Shriram's book).

I get an error:
/snip/
setup-plt: --- creating launchers ---
setup-plt: --- installing collections ---
setup-plt: --- post-installing collections ---
setup-plt: done
setup-plt:
setup-plt: error: during making for <user>/plai (PLAI)
setup-plt:   web/server.ss:81:8: module: identifier is already  
imported at: url->path in: (define-values (url->path) (fsmap:make-url- 
 >path (build-path server-root-path "htdocs")))
setup-plt: error: during making for <user>/plai/web
setup-plt:   server.ss:81:8: module: identifier is already imported  
at: url->path in: (define-values (url->path) (fsmap:make-url->path  
(build-path server-root-path "htdocs")))

any idea?

-- Éric