When you run CPUU against an Outlook profile, it is not updated and the following error is in the log:
2004/12/24 14:31:03 Core [Info] Default mail client: Outlook Express.
2004/12/24 14:31:03 Core [Info] Temporarily changing the default mail client to 'Microsoft Outlook'.
2004/12/24 14:31:03 Core [Error] Cannot set default mail client.
Standard error.
Error code: 0x00000005
Description: Access is denied.
This issue is covered in CPUU release notes:
* CPUU may fail to update a profile if Microsoft Outlook is not the default mail client on the computer.
When Outlook is not the default mail client on the system, CPUU is trying to temporarily set the default mail client to Outlook which is necessary to process the profile. In order to make this change local administrative rights on the computer are required. If CPUU is running under account without local administrative rights and the default mail client is not Outlook the above error will be logged.
To resolve this issue run CPUUunder account which has enough permissions on the computer. Alternatively you can give the account CPUU is running under Full Control permissions on the HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail registry key. If many workstations need these permission to be changed, a group policy can be easily configured to do so.