Fed8 to Fed9 update broke yum but I need it to fix the install

I just want to do a yum update but yum itself is broken. Heres what I get:

[root@tiger ~]# yum
error: no dbpath has been set
error: cannot open Packages database in /%{_dbpath}
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 241, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 96, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 182, in getOptionsConfig
    disabled_plugins=self.optparser._splitArg(opts.disableplugins))
  File "/usr/lib/python2.5/site-packages/yum/__init__.py", line 180, in 
_getConfig
    self._conf = config.readMainConfig(startupconf)
  File "/usr/lib/python2.5/site-packages/yum/config.py", line 735, in 
readMainConfig
    yumvars['releasever'] = _getsysver(startupconf.installroot, 
startupconf.distroverpkg)
  File "/usr/lib/python2.5/site-packages/yum/config.py", line 802, in 
_getsysver
    idx = ts.dbMatch('provides', distroverpkg)
TypeError: rpmdb open failed

This worked fine in Fed 8. Has anyone seen this before or got any 
suggestions please? Thanks