Install finished (Error 0x80004005: Unspecified error)

I am having problems when trying to install updates already downloaded via
Automatic Updates on my Windows XP Clients.
We are using Software Update Services and no XP client could update
correctly the automatic updates although 2000 clients updates could.

The updates reaches my client and download correctly, later i get notified
about those new updates but when I command to install the updates Windows
tells me everything OK.

But...

After checking my Windows Update.Log
I got the line from the Subject so I know updates are not being installed.

Any ideas.