On a number of Vista machines I have now come across the same error - when installing updates everything works fine, until it after it reboots and the rolls back during step 3. On all occasions (where a simple retry hasn't worked) the error code has been 800719e4.
On my own laptop I have so far tried the following:-
Installed the updates one by one manually - I started on the smallest and one by one have worked towards the largest one which has left me with "Security Update for Windows (KB2286198)" that refuses to install.
Renamed all the files in "C:\Windows\Logs\CBS" to "xxx.old" where xxx was the original name with windows update turned off - no change
Renamed all the folders in "C:\Windows\SoftwareDistribution" in the same manner - no change
Attempted to install it manually "Windows6.0-KB2286198-x86.msu" - no change
Tried to un-install IE8 - doesn't work, rolls back at the end (Installing the IE9 Beta when it launched was what alerted me to the issue on this laptop)
Ran a "Fix It" thing from the Microsoft Website - no help (Can't find the link now).
Tried to recover from the disk - but alas my laptop only has a recovery partition (and was unservice packed original).
Ran with nothing running on startup, and only MS services - again no change.
Google is being useless with a load of posts trying to get me to call a telephone number with letters in (presumably an American number)
The error code appears to mean error log full but no one has any idea which log! The WinUpdate log does indicate the following is the error point though :-
2010-10-23 13:54:48:230 1240 738 Handler WARNING: Got extended error: "POQ Operation SetKeyValue OperationData \Registry\machine\Schema\wcm://Microsoft-Windows-shell32?version=6.0.6002.18287&language=neutral&processorArchitecture=x86&publicKeyToken=31bf3856ad364e35&versionScope=nonSxS&scope=allUsers\metadata\elements\HKEY_CLASSES_ROOT_lnkfile_shellex_DropHandler_defaultValue, @default, , ewAwADAAMAAyADEANAAwADEALQAwADAAMAAwAC0AMAAwADAAMAAtAEMAMAAwADAALQAwADAAMAAwADAAMAAwADAAMAAwADQANgB9AAAA"
Has anyone any idea how to fix this once and for all - reinstalling laptop after laptop from scratch is mildly annoying at work where Office and Firefox are the only extras, but even more annoying at home - I don't fancy going through the palaver of reinstalling everything yet again.