Managed DirectX update - Install failure

I have been using Windows Update to "scan for updates",
download fixes from MS and install them on my PC.

Recently I selected the Managed DirectX update. It
downloaded OK but the Install stage failed with no
indication of the problem). I tried the update a second
time. The download stage detected that the changes were
already present on my PC and so did not try to download
them again. The Install stage failed again.

Has anyone any views on how I can sort out the problem?

I successfully installed DirectX 9.0a End-User Runtime
from the MS Website on 17 May.

I have run the "dxdiag" command which did not detect any
problems with my DirectX software.
DirectX Version: DirectX 9.0a (4.09.0000.0901)

I also found a DirectX.log which showed that the Install
had not proceeded. There were several lines of the form -
06/26/03 11:13:53: mdxsetup: IsAssemblyInUse():
Microsoft.DirectX.DirectSound:1.0.900.0:31bf3856ad 364e35
is not locked

then -
06/26/03 11:13:54: mdxsetup: Managed DirectX Version:
4.09.00.0900
06/26/03 11:13:54: mdxsetup: MDX version was not updated.

thanks in advance