Error: 0x80240018

While trying to access http://update.microsoft.com from a Windows XP SP2
machine, I get error 0x80240018.

I am behind an ISA proxy. But another machine with same OS is able to get
updates from the same site.

WindowsUpdate.log snippet
--------------------------------
2005-06-09 18:12:52 852 488 Agent ** START ** Agent: Finding updates
[CallerId = MicrosoftUpdate]
2005-06-09 18:12:52 852 488 Agent *********
2005-06-09 18:12:52 852 488 Misc WARNING: Failed to find token for SID
S-1-5-21-1482476501-1844823847-839522115-500 with hr = 80240018.
2005-06-09 18:12:52 852 488 Misc WARNING: Failed to find token for SID
S-1-5-21-1482476501-1844823847-839522115-500 with hr = 80240018.
2005-06-09 18:12:52 852 488 Misc WARNING: Send failed with hr = 80240018.
2005-06-09 18:12:52 852 488 Misc WARNING: SendRequest failed with hr =
80240018. Proxy List used: <my_ISA_proxy_IP_here> Bypass List used : <(null)>
Auth Schemes used : <NTLM;Negotiate (NTLM or Kerberos);>
2005-06-09 18:12:52 852 488 Misc WARNING: WinHttp: SendRequestUsingProxy
failed for
<http://download.windowsupdate.com/v6/microsoftupdate/redir/muredir.cab>.
error 0x80240018
2005-06-09 18:12:52 852 488 Misc WARNING: WinHttp:
SendRequestToServerForFileInformation MakeRequest failed. error 0x80240018
2005-06-09 18:12:52 852 488 Misc WARNING: WinHttp:
SendRequestToServerForFileInformation failed with 0x80240018
2005-06-09 18:12:52 852 488 Misc WARNING: WinHttp: ShouldFileBeDownloaded
failed with 0x80240018

--------------------------------
This repeats itself and finally concludes with
--------------------------------
2005-06-09 18:12:52 852 488 Misc WARNING: DownloadFileInternal failed for
http://update.microsoft.com/v6/micro...r/muredir.cab: error
0x80240018
2005-06-09 18:12:52 852 488 Agent * WARNING: Failed to synchronize, error
= 0x80240018
2005-06-09 18:12:52 852 488 Agent * WARNING: Exit code = 0x80240018
2005-06-09 18:12:52 852 488 Agent *********
2005-06-09 18:12:52 852 488 Agent ** END ** Agent: Finding updates
[CallerId = MicrosoftUpdate]
2005-06-09 18:12:52 852 488 Agent *************
2005-06-09 18:12:52 852 488 Agent WARNING: WU client failed Searching for
update with error 0x80240018
2005-06-09 18:12:53 2316 46c COMAPI >>-- RESUMED -- COMAPI: Search
[ClientId = MicrosoftUpdate]
2005-06-09 18:12:53 2316 46c COMAPI - Updates found = 0
2005-06-09 18:12:53 2316 46c COMAPI - WARNING: Exit code = 0x00000000,
Result code = 0x80240018
2005-06-09 18:12:53 2316 46c COMAPI ---------
2005-06-09 18:12:53 2316 46c COMAPI -- END -- COMAPI: Search [ClientId =
MicrosoftUpdate]
2005-06-09 18:12:53 2316 46c COMAPI -------------
2005-06-09 18:12:53 2316 9cc COMAPI WARNING: Operation failed due to earlier
error, hr=80240018
2005-06-09 18:12:53 2316 9cc COMAPI FATAL: Unable to complete asynchronous
search. (hr=80240018)
2005-06-09 18:12:57 852 488 Report REPORT EVENT:
{714865C0-3A8C-4AC6-80EF-B03054D5F31C} 2005-06-09
18:12:52+0530 1 148 101 {00000000-0000-0000-0000-000000000000} 0 80240018 MicrosoftUpdate Failure Software Synchronization

--------------------------------

Anybody knows what this indicates?

Thanks,