本文是早晨诗雨同学早晨在KB中找到的内容，之前和十一同学也讨论过，既然有KB了我就转贴出来，呵呵，我也碰到过此类情况。
微软KB的地址：http://support.microsoft.com/kb/947284/en-us
解决办法就是在SharePoint管理中心中给应用程序池更换服务帐号即可解决。但其中什么原因造成的却是不太明白。
以下为原文内容：
 

A declarative workflow does not start automatically after you install Windows SharePoint Services 3.0 Service Pack 1

View products that this article applies to.
Article ID : 947284
Last Review : February 1, 2008
Revision : 1.1

SYMPTOMS

After you install Windows SharePoint Services 3.0 Service Pack 1 (SP1), a declarative workflow does not start automatically in the following products:
• Windows SharePoint Services 3.0
• Microsoft Office SharePoint Server 2007
• Microsoft Office SharePoint Designer 2007
For example, if you configure a declarative workflow to start when a new item is created or when a new item is changed, the declarative workflow does not start as expected. The Unified Logging Service (ULS) log files contain no information about why this behavior occurs.
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CAUSE

This behavior occurs because a security fix in Windows SharePoint Services 3.0 SP1 prevents declarative workflows from starting automatically under the system account. After you install Windows SharePoint Services 3.0 SP1, declarative workflows do not start automatically if the following conditions are true:
• The Windows SharePoint Services Web application runs under a user's domain account.
• The user logs in by using this domain account.
• The site displays the user name as System Account.
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RESOLUTION

To resolve this behavior, set the application pool account to use a different user account. You may want to create a new user account specifically for this purpose.

To set the application pool account to use a different user account, follow these steps:
1. On the server that is running one of the products that is listed in the "Applies to" section, click Start, point to All Programs, point to Microsoft Office Server, and then click SharePoint 3.0 Central Administration.
2. Click the Operations tab.
3. Under Security Configuration, click Service Accounts.
4. Click Web application pool, and then click Windows SharePoint Services Web Application in the Web service box.
5. In the Application pool box, click the application pool that you want to change.
6. Under Select an account for this component, click Configurable, and then type the user name and the password for the different user account.
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STATUS

This behavior is by design.
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APPLIES TO
• Microsoft Windows SharePoint Services 3.0
• Microsoft Office SharePoint Designer 2007
• Microsoft Office SharePoint Server 2007
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Keywords: 
 kbtshoot kbexpertiseadvanced kbnofix kbprb KB947284
Tag标签: MOSS, SP1, WSS