windows update无法更新，提示0x80244021的解决方法

最近发现公司的一台windows7的电脑无法自动更新，点击“检查更新”按钮时，提示0x80244021错误。windows update.log日志如下：

2011-11-08  09:51:13:363     972    13d8    AU  Triggering AU detection through DetectNow API
2011-11-08  09:51:13:363     972    13d8    AU  Triggering Online detection (interactive)
2011-11-08  09:51:13:363     972    a10 AU  #############
2011-11-08  09:51:13:363     972    a10 AU  ## START ##  AU: Search for updates
2011-11-08  09:51:13:363     972    a10 AU  #########
2011-11-08  09:51:13:363     972    a10 AU  <<## SUBMITTED ## AU: Search for updates [CallId = {1436F467-82EE-4DED-A72D-5694818E7E49}]
2011-11-08  09:51:13:363     972    2b54    Agent   *************
2011-11-08  09:51:13:363     972    2b54    Agent   ** START **  Agent: Finding updates [CallerId = AutomaticUpdates]
2011-11-08  09:51:13:363     972    2b54    Agent   *********
2011-11-08  09:51:13:363     972    2b54    Agent     * Online = Yes; Ignore download priority = No
2011-11-08  09:51:13:363     972    2b54    Agent     * Criteria = "IsInstalled=0 and DeploymentAction='Installation' or IsPresent=1 and DeploymentAction='Uninstallation' or IsInstalled=1 and DeploymentAction='Installation' and RebootRequired=1 or IsInstalled=0 and DeploymentAction='Uninstallation' and RebootRequired=1"
2011-11-08  09:51:13:363     972    2b54    Agent     * ServiceID = {3DA21691-E39D-4DA6-8A4B-B43877BCB1B7} Managed
2011-11-08  09:51:13:363     972    2b54    Agent     * Search Scope = {Machine}
2011-11-08  09:51:13:363     972    2b54    Setup   Checking for agent SelfUpdate
2011-11-08  09:51:13:363     972    2b54    Setup   Client version: Core: 7.5.7601.17514  Aux: 7.5.7601.17514
2011-11-08  09:51:13:363     972    2b54    Misc    Validating signature for C:\windows\SoftwareDistribution\SelfUpdate\wuident.cab:
2011-11-08  09:51:13:378     972    2b54    Misc     Microsoft signed: Yes
2011-11-08  09:51:13:409     972    2b54    Misc    WARNING: WinHttp: SendRequestToServerForFileInformation failed with 0x801901f6
2011-11-08  09:51:13:409     972    2b54    Misc    WARNING: WinHttp: ShouldFileBeDownloaded failed with 0x801901f6
2011-11-08  09:51:13:409     972    2b54    Misc    WARNING: DownloadFileInternal failed for http://172.16.160.236:8530/selfupdate/wuident.cab: error 0x801901f6
2011-11-08  09:51:13:409     972    2b54    Setup   WARNING: SelfUpdate check failed to download package information, error = 0x80244021
2011-11-08  09:51:13:409     972    2b54    Setup   FATAL: SelfUpdate check failed, err = 0x80244021
2011-11-08  09:51:13:409     972    2b54    Agent     * WARNING: Skipping scan, self-update check returned 0x80244021
2011-11-08  09:51:13:409     972    2b54    Agent     * WARNING: Exit code = 0x80244021
2011-11-08  09:51:13:409     972    2b54    Agent   *********
2011-11-08  09:51:13:409     972    2b54    Agent   **  END  **  Agent: Finding updates [CallerId = AutomaticUpdates]
2011-11-08  09:51:13:409     972    2b54    Agent   *************
2011-11-08  09:51:13:409     972    2b54    Agent   WARNING: WU client failed Searching for update with error 0x80244021
2011-11-08  09:51:13:409     972    2148    AU  >>##  RESUMED  ## AU: Search for updates [CallId = {1436F467-82EE-4DED-A72D-5694818E7E49}]
2011-11-08  09:51:13:409     972    2148    AU    # WARNING: Search callback failed, result = 0x80244021
2011-11-08  09:51:13:409     972    2148    AU    # WARNING: Failed to find updates with error code 80244021
2011-11-08  09:51:13:409     972    2148    AU  #########
2011-11-08  09:51:13:409     972    2148    AU  ##  END  ##  AU: Search for updates [CallId = {1436F467-82EE-4DED-A72D-5694818E7E49}]
2011-11-08  09:51:13:409     972    2148    AU  #############

公司的环境是这样的：所有客户端电脑通过内部的WSUS服务器（172.16.160.236）更新补丁，使用ISA server2006代理上网，部分电脑安装有ISA防火墙客户端软件。

发现问题的这台windows7上安装有ISA防火墙客户端。

解决方法：

在这台有问题的windows7上，打开cmd命令提示符窗口，输入：

netsh winhttp set proxy proxy-server="http=isasvr.xxx.com:8080" bypass-list="172.16.160.236"

以上命令的作用为，与内部WSUS服务器之间的通讯不经过ISA代理服务器，也就是直接从WSUS服务器更新。