yum update dies in error 'TypeError: unsubscriptable object'... yum clean all

While updating one of my servers today I entered this command yum update file and received the following error message.

Traceback (most recent call last): File "/usr/bin/yum", line 29, in ? yummain.user_main(sys.argv[1:], exit_code=True) File "/usr/share/yum-cli/yummain.py", line 229, in user_main errcode = main(args) File "/usr/share/yum-cli/yummain.py", line 145, in main (result, resultmsgs) = base.buildTransaction() File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 647, in buildTransaction (rescode, restring) = self.resolveDeps() File "/usr/lib/python2.4/site-packages/yum/depsolve.py", line 704, in resolveDeps for po, dep in self._checkFileRequires(): File "/usr/lib/python2.4/site-packages/yum/depsolve.py", line 939, in _checkFileRequires if not self.tsInfo.getOldProvides(filename) and not self.tsInfo.getNewProvides(filename): File "/usr/lib/python2.4/site-packages/yum/transactioninfo.py", line 414, in getNewProvides for pkg, hits in self.pkgSack.getProvides(name, flag, version).iteritems(): File "/usr/lib/python2.4/site-packages/yum/packageSack.py", line 300, in getProvides return self._computeAggregateDictResult("getProvides", name, flags, version) File "/usr/lib/python2.4/site-packages/yum/packageSack.py", line 470, in _computeAggregateDictResult sackResult = apply(method, args) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 861, in getProvides return self._search("provides", name, flags, version) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 43, in newFunc return func(*args, **kwargs) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 837, in _search for pkg in self.searchFiles(name, strict=True): File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 43, in newFunc return func(*args, **kwargs) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 586, in searchFiles self._sql_pkgKey2po(rep, cur, pkgs) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 470, in _sql_pkgKey2po pkg = self._packageByKey(repo, ob['pkgKey']) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 413, in _packageByKey po = self.pc(repo, cur.fetchone()) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 68, in __init__ self._read_db_obj(db_obj) File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 94, in _read_db_obj setattr(self, item, _share_data(db_obj[item])) TypeError: unsubscriptable object

This happened every time until I cleaned the cache.

yum clean all

Then it worked without a flaw.