[racket] error from web-server tutorial

re: http://download.plt-scheme.org/doc/4.2.1/html/continue/index.html

hello,

i am having trouble getting to run the 1st example in 
tutorial "Continue: Web Applications in PLT Scheme", here:

  #lang web-server/insta
  (define (start request)
   '(html
     (head (title "My Blog"))
     (body (h1 "Under construction"))))


what is returned is following web page at
  http://localhost:2906/servlets/standalone.rkt

Exception
The application raised an exception with the message:

self-contract violation: expected <can-be-response?>, given: '(html
(head (title "My Blog")) (body (h1 "Under construction")))
  contract on start from you, blaming you
  contract: 
    (-> request? can-be-response?)

Stack trace:

raise-blame-error at:
  line 58, column 0, in file H:\Program
  Files\Racket\collects\racket\contract\private\blame.rkt
<unknown procedure> at:
  line 58, column 2, in file H:\Program
  Files\Racket\collects\web-server\dispatchers\dispatch-servlets.rkt
select-handler/no-breaks at:
  line 164, column 2, in file H:\Program
  Files\Racket\collects\racket\private\more-scheme.rkt
connection-loop at:
  line 74, column 2, in file H:\Program
  Files\Racket\collects\web-server\private\dispatch-server-unit.rkt


i am using racket 5.1


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