[racket] problem with database connectivity

Regardless of using a postgresql or a mysql database server the following error message

  ptr-ref: contract violation
   expected: ctype?
   given: #<void>
   argument position: 2nd
   other arguments...:
    #<ffi-obj>

appears when trying to connect it from drracket by

#lang racket
(require db)

(define dbc1
   (postgresql-connect #:user "postgres"
                       #:database "postgres"
                       #:password "abcd"
                       #:server "localhost"
                       #:port 5432))

I ensured to have the 64 bit versions of the systems installed under Win 7.
Thanks for your help in advance, Christian

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