Impossible d'installer IE7

[Salutationsdistinguées]

Salut à tous,

Je galère énormément pour installer IE7.

L'installation est refusée, voici le log qui suit:
IECUSTOM: Scanning for proper registry permissions...
4.453: IECUSTOM: Unwriteable key HKCR\prffile
4.453: IECUSTOM: Unwriteable key HKCR\prffile
4.453: IECUSTOM: Unwriteable key HKCR\prffile\DefaultIcon
4.453: IECUSTOM: Unwriteable key HKCR\prffile
4.453: IECUSTOM: Unwriteable key HKCR\prffile\shell
4.453: IECUSTOM: Unwriteable key HKCR\prffile
4.453: IECUSTOM: Unwriteable key HKCR\prffile\shell\Open\command
4.453: IECUSTOM: Unwriteable key HKCR\prffile\shell\Open
4.453: IECUSTOM: Unwriteable key HKCR\prffile\shell
4.453: IECUSTOM: Unwriteable key HKCR\prffile
5.437: IECUSTOM: Scanning for proper registry permissions...
5.672: IECUSTOM: Scanning for proper registry permissions...
6.406: IECUSTOM: Unwriteable key HKCR\prffile
6.406: IECUSTOM: Unwriteable key HKCR\prffile
6.406: IECUSTOM: Unwriteable key HKCR\prffile\DefaultIcon
6.406: IECUSTOM: Unwriteable key HKCR\prffile
6.406: IECUSTOM: Unwriteable key HKCR\prffile\shell
6.406: IECUSTOM: Unwriteable key HKCR\prffile
6.406: IECUSTOM: Unwriteable key HKCR\prffile\shell\Open\command
6.406: IECUSTOM: Unwriteable key HKCR\prffile\shell\Open
6.406: IECUSTOM: Unwriteable key HKCR\prffile\shell
6.406: IECUSTOM: Unwriteable key HKCR\prffile
6.547: IECUSTOM: Backing up registry permissions...
6.609: IECUSTOM: Finished backing up registry permissions...
6.609: IECUSTOM: Setting new registry permissions...
6.609: IECUSTOM: Unable to clear DACLs HKCR\prffile
6.609: IECUSTOM: Finished setting new registry permissions...
6.609: IECUSTOM: An error occured verifying registry permissions. ERROR: 0x80070534
6.609: DoInstallation: CustomizeCall Failed: 0x3f5
6.641: IECUSTOM: Restoring registry permissions...
6.672: IECUSTOM: Finished restoring registry permissions...
6.703: Impossible d'écrire la clé du Registre de configuration.
6.703: L'installation du Internet Explorer 7 ne s'est pas terminée.
6.703: Update.exe extended error code = 0x3f5

J'ai mis toutes les permissions sur les clés concernées et ça ne fonctionne toujours pas.
Merci pour votre aide