ghc can't find libraries for non-standard install

(tromp 999) ghci -v
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.4.20050301, for Haskell 
98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.
 
Reading package config file: 
/export/scratch1/tromp/lib/ghc-6.4.20050301/package.conf
Hsc static flags: -static
*** Parser:
 
<interactive>:1:22:
    Failed to load interface for `System.IO':
        Could not find module `System.IO':
          locations searched: 
/usr/local/lib/ghc-6.4.20050301/imports/System/IO.hi
*** Deleting temp files
Deleting:
ghc-6.4.20050301: panic! (the `impossible' happened, GHC version 6.4.20050301):
        interactiveUI:setBuffering
 
Please report it as a compiler bug to glasgow-haskell-bugs@xxxxxxxxxxx,
or http://sourceforge.net/projects/ghc/.

(tromp 1000) uname -a
Linux capella.ins.cwi.nl 2.6.8-1.521 #1 Mon Aug 16 09:01:18 EDT 2004 i686 
athlon i386 GNU/Linux



PS: the directory /usr/local/lib/ghc-6.4.20050301 does not exist.
    I don't understand why it searches there.
    I configured with ./configure --prefix=/export/scratch1/tromp/
regards,

%!PS                       %  -John Tromp (http://www.cwi.nl/~tromp/)
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