non riesco a modificare le autorizzazioni nel registro

[cesareco]

ho windows xp sp3, e sono amministratore e singolo utente di un singolo computer.

non riesco a installare internet explorer 8; il file: ie8.log mi dice che la installazione non è riuscita per divieto di accesso a un elenco di chiavi del registro.
trascrivo il log, per chiarezza.
il problema è il seguente:
certe chiavi non si modificano, sia avviando windows in modalità normale che provvisoria; appena clicco sulla voce del regedit, appare la scritta: impossibile aprire / accesso negato; col mouse destro clicco su: autorizzazioni, e una finestra dice che l'utente non è autorizzato a visualizzare o modificare le impostazioni.

chiedo la cortesia di un suggerimento, per una soluzione.
grazie.

[ie8.log]
0.297: ================================================== ==============================
0.297: 2009/05/01 19:21:35.015 (local)
0.297: h:\eb714cd8e1a9c73e3a2221d2\update\update.exe (version 6.3.15.0)
0.329: Hotfix started with following command line: /quiet /norestart /er /log:C:\WINDOWS
0.329: In Function GetReleaseSet, line 1240, RegQueryValueEx failed with error 0x2
0.344: IECUSTOM: Scanning for proper registry permissions...
0.579: IECUSTOM: Unwriteable key HKCR\.application\bootstrap
0.579: IECUSTOM: Unwriteable key HKCR\.hqx
0.579: IECUSTOM: Unwriteable key HKCR\.prf
0.579: IECUSTOM: Unwriteable key HKCR\.prf
0.797: IECUSTOM: Unwriteable key HKCR\Interface\{34A715A0-6587-11D0-924A-0020AFC7AC4D}
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_SQM_U PLOAD_FOR_APP
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_SQM_U PLOAD_FOR_APP
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_UNICO DE_HANDLE_CLOSING_CALLBACK
0.907: IECUSTOM: Unwriteable key HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_ENABLE_SCRIPT _PASTE_URLACTION_IF_PROMPT
0.907: IECUSTOM: Unwriteable key HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_ENABLE_SCRIPT _PASTE_URLACTION_IF_PROMPT
0.907: IECUSTOM: Unwriteable key HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_ENABLE_SCRIPT _PASTE_URLACTION_IF_PROMPT
0.907: IECUSTOM: Unwriteable key HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_IGNORE_XML_PR OLOG
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_INTERNET_SHEL L_FOLDERS
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_LEGACY_DISPPA RAMS
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_SUBDOWNLOAD_L OCKDOWN
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_SUBDOWNLOAD_L OCKDOWN
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_SUBDOWNLOAD_L OCKDOWN
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
0.907: IECUSTOM: Unwriteable key HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_WEBOC_MOVESIZ ECHILD
0.907: IECUSTOM: Unwriteable key HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_WEBOC_MOVESIZ ECHILD
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
0.907: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
1.000: IECUSTOM: Scanning for proper registry permissions...
1.219: IECUSTOM: Scanning for proper registry permissions...
1.438: IECUSTOM: Unwriteable key HKCR\.application\bootstrap
1.438: IECUSTOM: Unwriteable key HKCR\.hqx
1.438: IECUSTOM: Unwriteable key HKCR\.prf
1.438: IECUSTOM: Unwriteable key HKCR\.prf
1.516: IECUSTOM: Unwriteable key HKCR\Interface\{34A715A0-6587-11D0-924A-0020AFC7AC4D}
1.547: IECUSTOM: Unwriteable key HKCR\xmlfile\DefaultIcon
1.563: IECUSTOM: Unwriteable key HKLM\SOFTWARE\Classes\xmlfile\DefaultIcon
1.610: IECUSTOM: Backing up registry permissions...
1.610: IECUSTOM: Unable to backup DACLs HKCR\.application\bootstrap
1.610: IECUSTOM: Finished backing up registry permissions...
1.610: IECUSTOM: An error occured verifying registry permissions. ERROR: 0x80070005
1.610: DoInstallation: CustomizeCall Failed: 0x3f5
1.610: IECUSTOM: Restoring registry permissions...
1.610: IECUSTOM: Unable to restore DACLs HKCR\.application\bootstrap
1.610: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
1.610: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\UrlTemplate
1.625: IECUSTOM: Unable to restore DACLs HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_WEBOC_MOVESIZ ECHILD
1.625: IECUSTOM: Unable to restore DACLs HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_WEBOC_MOVESIZ ECHILD
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_USE_WINDOWEDS ELECTCONTROL
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_SUBDOWNLOAD_L OCKDOWN
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_SUBDOWNLOAD_L OCKDOWN
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_SUBDOWNLOAD_L OCKDOWN
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_LEGACY_DISPPA RAMS
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_INTERNET_SHEL L_FOLDERS
1.625: IECUSTOM: Unable to restore DACLs HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_IGNORE_XML_PR OLOG
1.625: IECUSTOM: Unable to restore DACLs HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_ENABLE_SCRIPT _PASTE_URLACTION_IF_PROMPT
1.625: IECUSTOM: Unable to restore DACLs HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_ENABLE_SCRIPT _PASTE_URLACTION_IF_PROMPT
1.625: IECUSTOM: Unable to restore DACLs HKLM\Software\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_ENABLE_SCRIPT _PASTE_URLACTION_IF_PROMPT
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_UNICO DE_HANDLE_CLOSING_CALLBACK
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_SQM_U PLOAD_FOR_APP
1.625: IECUSTOM: Unable to restore DACLs HKLM\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_DISABLE_SQM_U PLOAD_FOR_APP
1.625: CustomizeCall:GetProcAddress for FailedInstallation failed: 0x3f0
1.625: Impossibile scrivere la chiave del Registro di sistema.
1.625: Internet Explorer 8 installation did not complete.
1.625: Update.exe extended error code = 0x3f5