SQL Server 2008 setup error: Attempted to perform an unauthorized operation

I'm trying to install SQL Server 2008 on a virtual machine with Windows 2008 R2.

Setup fails with the error "Attempted to perform an unauthorized operation".

Looking at the installation log, I see these details:

2009-09-29 08:24:49 SQLBrowser: sRegLocation = 'SOFTWARE\Microsoft\Microsoft SQL Server', regView = 'Wow6432', sSddl = '(A;CI;KR;;;[SQLServer2005SQLBrowserUser$ITISFIM])', bOptional = 'False'.
2009-09-29 08:24:49 Slp: Sco: Attempting to create base registry key HKEY_LOCAL_MACHINE, machine 
2009-09-29 08:24:49 Slp: Sco: Attempting to open registry subkey 
2009-09-29 08:24:49 Slp: Sco: Attempting to open registry subkey SOFTWARE\Microsoft\Microsoft SQL Server
2009-09-29 08:24:49 Slp: Sco: Attempting to replace account with sid in security descriptor (A;CI;KR;;;[SQLServer2005SQLBrowserUser$ITISFIM])
2009-09-29 08:24:49 Slp: ReplaceAccountWithSidInSddl -- SDDL to be processed:  (A;CI;KR;;;[SQLServer2005SQLBrowserUser$ITISFIM])
2009-09-29 08:24:49 Slp: Sco: Account name to be translated into SID: SQLServer2005SQLBrowserUser$ITISFIM
2009-09-29 08:24:49 Slp: Sco: Attempting to get account sid for user account SQLServer2005SQLBrowserUser$ITISFIM
2009-09-29 08:24:49 Slp: Sco: Attempting to get sid for user account SQLServer2005SQLBrowserUser$ITISFIM
2009-09-29 08:24:49 Slp: Sco: GetSidForAccount normalized accountName SQLServer2005SQLBrowserUser$ITISFIM parameter to SQLServer2005SQLBrowserUser$ITISFIM
2009-09-29 08:24:49 Slp: Sco: Account name is translated into: S-1-5-21-3278988706-2344661944-1675463508-1000
2009-09-29 08:24:49 Slp: Sco: Final security descriptor:  (A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: Sco: Attempting to set security descriptor (A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: Sco: Attempting to normalize security descriptor (A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: Sco: Adding 'D:' DACL identifier to the input security descriptor (A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: Sco: Attempting to replace account with sid in security descriptor D:(A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: ReplaceAccountWithSidInSddl -- SDDL to be processed:  D:(A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: ReplaceAccountWithSidInSddl -- SDDL to be returned:  D:(A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: Sco: Attempting to normalize security descriptor D:(A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: Sco: Attempting to replace account with sid in security descriptor D:(A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: ReplaceAccountWithSidInSddl -- SDDL to be processed:  D:(A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: ReplaceAccountWithSidInSddl -- SDDL to be returned:  D:(A;CI;KR;;;S-1-5-21-3278988706-2344661944-1675463508-1000)
2009-09-29 08:24:49 Slp: Prompting user if they want to retry this action due to the following failure:
2009-09-29 08:24:49 Slp: ----------------------------------------
2009-09-29 08:24:49 Slp: The following is an exception stack listing the exceptions in outermost to innermost order
2009-09-29 08:24:49 Slp: Inner exceptions are being indented
2009-09-29 08:24:49 Slp: 
2009-09-29 08:24:49 Slp: Exception type: Microsoft.SqlServer.Configuration.Sco.ScoException
2009-09-29 08:24:49 Slp:     Message: 
2009-09-29 08:24:49 Slp:         Attempted to perform an unauthorized operation.
2009-09-29 08:24:49 Slp:     Data: 
2009-09-29 08:24:49 Slp:       WatsonData = Microsoft SQL Server
2009-09-29 08:24:49 Slp:       DisableRetry = true
2009-09-29 08:24:49 Slp:     Inner exception type: System.UnauthorizedAccessException
2009-09-29 08:24:49 Slp:         Message: 
2009-09-29 08:24:49 Slp:                 Attempted to perform an unauthorized operation.
2009-09-29 08:24:49 Slp:         Stack: 
2009-09-29 08:24:49 Slp:                 at System.Security.AccessControl.Win32.GetSecurityInfo(ResourceType resourceType, String name, SafeHandle handle, AccessControlSections accessControlSections, RawSecurityDescriptor& resultSd)
2009-09-29 08:24:49 Slp:                 at System.Security.AccessControl.NativeObjectSecurity.CreateInternal(ResourceType resourceType, Boolean isContainer, String name, SafeHandle handle, AccessControlSections includeSections, Boolean createByName, ExceptionFromErrorCode exceptionFromErrorCode, Object exceptionContext)
2009-09-29 08:24:49 Slp:                 at Microsoft.SqlServer.Configuration.Sco.SqlRegistrySecurity..ctor(ResourceType resourceType, SafeRegistryHandle handle, AccessControlSections includeSections)
2009-09-29 08:24:49 Slp:                 at Microsoft.SqlServer.Configuration.Sco.SqlRegistrySecurity.Create(InternalRegistryKey key)
2009-09-29 08:24:49 Slp:                 at Microsoft.SqlServer.Configuration.Sco.InternalRegistryKey.SetSecurityDescriptor(String sddl, Boolean overwrite)
2009-09-29 08:24:49 Slp: ----------------------------------------

Any suggestions on how to fix this error?
Thanks, Paolo