Why does 'rhn_check' fail with the error "ImportError: No module named cElementTree" in Red Hat Enterprise Linux?

Issue

• Running 'rhn_check' fails with the following error:

# rhn_check
Traceback (most recent call last):
  File "/usr/sbin/rhn_check", line 21, in ?
    from up2date_client import up2dateErrors
  File "/usr/share/rhn/up2date_client/up2dateErrors.py", line 14, in ?
    from yum.Errors import RepoError, YumBaseError
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 50, in ?
    import comps
  File "/usr/lib/python2.4/site-packages/yum/comps.py", line 22, in ?
    import cElementTree
ImportError: No module named cElementTree