GHCi Package problem?

I encountered the following problem while loading a package,
and ghci (version 6.2) told me to report it to this list.

  Loading package fgl ... linking ...
  /usr/local/lib/ghc-6.2/HSfgl.o: unknown symbol 
`_DataziTree_flatten_entry'
  ghc-6.2: panic! (the `impossible' happened, GHC version 6.2):
          can't load package `fgl'

  Please report it as a compiler bug to 
glasgow-haskell-bugs@xxxxxxxxxxx,
  or http://sourceforge.net/projects/ghc/.

This happened after I removed "base" from the package_deps entry (see 
below).

Package {
  name = "fgl",
  auto = True,
  import_dirs = ["$libdir/imports"],
  source_dirs = [],
  library_dirs = ["$libdir"],
  hs_libraries = ["HSfgl"],
  extra_libraries = [],
  include_dirs = [],
  c_includes = [],
  package_deps = ["base"],
  extra_ghc_opts = ["-fglasgow-exts"],
  extra_cc_opts = [],
  extra_ld_opts = [],
  framework_dirs = [],
  extra_frameworks = []
}

When "base" is included, ghci start fine:

  Loading package base ... linking ... done.
  Loading package fgl ... linking ... done.
  Prelude>

I can even access some values:

  Prelude> Data.Graph.Inductive.version

  FGL - Functional Graph Library, February 2005

However, when I try others, I get errors:

  Prelude> Data.Graph.Inductive.Example.clr486

  GHCi runtime linker: fatal error: I found a duplicate definition for 
symbol
     _DataziGraphziInductiveziInternalziFiniteMap_Empty_closure
  whilst processing object file
     ./Data/Graph/Inductive/Internal/FiniteMap.o
  This could be caused by:
     * Loading two different object files which export the same symbol
     * Specifying the same object file twice on the GHCi command line
     * An incorrect `package.conf' entry, causing some object to be
       loaded twice.
  GHCi cannot safely continue in this situation.  Exiting now.  Sorry.


I don't know what to do about this.


--
Martin