[plt-scheme] confusing error message

Greetings, all.

I've got a confusing error message (DrScheme CVS as of 23 Dec) that I'm
hoping someone can explain.

In the file bar.ss:

(module bar mzscheme
  (require "clinger.ss")
  
  (define ns (module->namespace "clinger.ss"))
  
  (define lookup
    (parameterize ([current-namespace ns])
      (namespace-variable-value 'lookup))))

The file clinger.ss, in the same directory, contains an implementation
of the macro expansion algorithm of Clinger and Rees (Clinger & Rees
1991).  This module defines lookup at top level, but it does not export
this identifier.

When I open bar.ss in DrScheme, under the module language level, and hit
execute, I get the following error message in the interactions window:

   require: broken compiled code (phase 0): cannot find module clinger
   in: lookup

Could someone tell me what that means, and what I need to do to get this
working?

I tried to boil this down to a toy example, using two very simple
modules, but I couldn't reproduce the problem.  I'm guessing, then, that
something in the clinger module, or one of its imports, may be causing
problems.  (More detail on that module as requested.)

Thanks for any advice,

Richard