When you attempt to install updates, you receive a 643 error or a message that indicates Windows Update could not complete the operation.
NOTE: You may also notice that Windows Media Player has become slow to respond.
These issues can be the result of a corrupt %SystemRoot%\system32\CatRoot2\Edb.log file, which may also grow to 20 megabytes.
NOTE: CatRoot2\Edb.log is normally less than 6 Megabytes.
To resolve this problem:
1. Open a CMD.EXE prompt.
del /q %SystemRoot%\System32\Catroot2\Edb.log
3. Press Enter to force the catalog database to rebuild itself.