Seg fault / memory error with yum 3.2 on redhat 5.5

Hello All,

I've got a redhat 5.5 machine which is supposedly up-to-date according
to RHN (yum-3.2.22-26.el5, python-2.4.3-27.el5). When I try to do
anything with yum, I get the following error:

---
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   /usr/lib64/python2.4/lib-dynload/_weakref.so: failed to map segment
from shared object: Cannot allocate memory

Please install a package which provides this module, or
verify that the module is installed correctly.

It's possible that the above module doesn't match the
current version of Python, which is:
2.4.3 (#1, Jun 11 2009, 14:09:37)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-44)]

If you cannot solve this problem yourself, please go to
the yum faq at:
  http://yum.baseurl.org/wiki/Faq
---

RHN verifies both the python and yum packages as correct, and as near as
I can tell the version of yum I have (yum-3.2.22-26.el5) should work
fine with the version of python (python-2.4.3-27.el5). What's more, I
have a separate brand new redhat machine with exactly the same versions
of the software installed, and yum works fine on that machine. If I
import the yum library into python myself I get a segmentation fault:

---
# python -vv
import zipimport # builtin
import site # precompiled from /usr/lib64/python2.4/site.pyc
import os # precompiled from /usr/lib64/python2.4/os.pyc
import posix # builtin
import posixpath # precompiled from /usr/lib64/python2.4/posixpath.pyc
import stat # precompiled from /usr/lib64/python2.4/stat.pyc
import errno # builtin
import UserDict # precompiled from /usr/lib64/python2.4/UserDict.pyc
import copy_reg # precompiled from /usr/lib64/python2.4/copy_reg.pyc
import types # precompiled from /usr/lib64/python2.4/types.pyc
import japanese # directory /usr/lib64/python2.4/site-packages/japanese
import japanese # precompiled from
/usr/lib64/python2.4/site-packages/japanese/__init__.pyc
import japanese.aliases # directory
/usr/lib64/python2.4/site-packages/japanese/aliases
import japanese.aliases # precompiled from
/usr/lib64/python2.4/site-packages/japanese/aliases/__init__.pyc
import encodings # directory /usr/lib64/python2.4/encodings
import encodings # precompiled from
/usr/lib64/python2.4/encodings/__init__.pyc
import codecs # precompiled from /usr/lib64/python2.4/codecs.pyc
import _codecs # builtin
import encodings.aliases # precompiled from
/usr/lib64/python2.4/encodings/aliases.pyc
import warnings # precompiled from /usr/lib64/python2.4/warnings.pyc
import linecache # precompiled from /usr/lib64/python2.4/linecache.pyc
import encodings.utf_8 # precompiled from
/usr/lib64/python2.4/encodings/utf_8.pyc
Python 2.4.3 (#1, Jun 11 2009, 14:09:37)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-44)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
dlopen("/usr/lib64/python2.4/lib-dynload/readline.so", 2);
import readline # dynamically loaded from
/usr/lib64/python2.4/lib-dynload/readline.so

>>> import yum
[vast swathes of successful imports snipped for space reasons]
import bisect # precompiled from /usr/lib64/python2.4/bisect.pyc
dlopen("/usr/lib64/python2.4/lib-dynload/_bisect.so", 2);
import _bisect # dynamically loaded from
/usr/lib64/python2.4/lib-dynload/_bisect.so
# trying cookielib.so
# trying cookielibmodule.so
# trying cookielib.py
# trying cookielib.pyc
# trying /usr/lib64/python24.zip/cookielib.so
# trying /usr/lib64/python24.zip/cookielibmodule.so
# trying /usr/lib64/python24.zip/cookielib.py
# trying /usr/lib64/python24.zip/cookielib.pyc
# trying /usr/lib64/python2.4/cookielib.so
# trying /usr/lib64/python2.4/cookielibmodule.so
# trying /usr/lib64/python2.4/cookielib.py
# /usr/lib64/python2.4/cookielib.pyc matches
/usr/lib64/python2.4/cookielib.py
Segmentation fault
---

I've tried googling round but can't find anyone else having a similar
problem; anyone have any suggestions? Thanks for any help,

- rob.