HKLM\Software\Microsoft\Windows\CurrentVersion\ Component Based Servicing\ApplicabilityEvaluationCache\ Package_for_KB947821~31bf3856ad364e35~xxx~~x.x.x.x
Fig 2.Dependce of system architecture and tool version the Package_for_KB947821 key have slightly different form
to delete Package_for_KB947821... first you have takewnership this -useful lecture CLICK
When everything is done,try again run Readiness Tool to diagnose your main problem with your OS.
STEP II -IF STEP I DOESN'T HELP....
1.Make sure you have enough free space on your disk.
2.Defrag your registry by using any good tool,I recommend registry defrag tool from Tune Up Utilities (unfortunately this soft is commrcial),from freeware tools I recommend QuickSys regDefrag
3.Uninstall all 3p security software
STEP III - IF NOTHING HELP...
Make sure you don't have any other system or hardware issues.If you have not empty C:\Windows\Minidump or C:\Windows\Memory.dmp then please analyze these files.Issues with RAM,hdd may also cause problem with running Readiness Tool and with installing normal updates.
System Manufacturer/Model Number Dell XPS 420 OS Vista Home Premium x86 SP2 CPU Intel Core 2 Quad Q9300 2.50GHz Motherboard Stock Dell 0TP406 Memory 4 gb (DDR2 800) 400MHz Graphics Card ATI Radeon HD 3870 (512 MBytes) Monitor(s) Displays 1 x Dell 2007FP and 1 x (old) Sonic flat screen Screen Resolution 1600 x 1200 and 1280 x 1204
Keyboard Dell Bluetooth Mouse Advent Optical ADE-WG01 (colour change light up) Case Dell XPS 420 Cooling Stock Fan Hard Drives 1 x 640Gb (SATA 300) Western Digital: WDC WD6400AAKS-75A7B0 1 x 1Tb (SATA 600) Western Digital: Caviar Black, SATA 6GB/S, 64Mb cache, 8ms Western Digital: WDC WD1002FAEX-00Z3A0 ATA Device Internet Speed Varies from 10kb/s to 170kb/s. So unreliable it is not funny Other Info ASUS USB 3.0 5Gbps/SATA 6Gbps - PCI-Express Combo Controller Card (U3S6)