[racket] handin server error

Hi all,

I am trying to set up the handin server -- spent some time at it last year, but gave up as the school year was already underway with its pressing demands -- and am getting this error when trying to hand in an assignment from a test account:

; --begin error message--
	submit error: Error in your code -- namespace-attach-module: a different module with the same name is already in the destination namespace module name: "/usr/local/racket/collects/scheme/base.rkt"
; --end error message--

It happens even with a trivially simple checker file:

;; sample checker.rkt file:
#lang s-exp handin-server/checker

(check: :language '(special beginner)
 )
;; end checker.rkt

I've been trying valiantly to troubleshoot on my own, but I've given more hours to the project than I can afford -- so, any suggestions where to look?

Thanks,
jmj