Be careful if plan to modify list items NEWitem.aspx !!!!!

Error message when you click "New" to create a new item in a list or when you click an existing item in SharePoint Server 2007 or in Windows SharePoint Services 3.0: "Invalid page URL" or "An unexpected error has occurred"
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Article ID : 935504
Last Review : June 5, 2007
Revision : 2.2
SYMPTOMS
Consider the following scenario. You use Microsoft Office SharePoint Designer 2007 to customize the NewForm.aspx page of a list in a Microsoft Office SharePoint Server 2007 site or in a Microsoft Windows SharePoint Services 3.0 site. Then, you connect to the list by using a Web browser. In this scenario, you experience the following symptoms:• If you click New to create a new item in the list, you receive the following message:
Invalid page URL:
• If you click an existing item in the list, you receive the following error message:
An unexpected error has occurred
Additionally, you might view the properties of the list in SharePoint Designer 2007 and then specify the NewForm.aspx page in the New item form box. When you do this, the NewForm.aspx page appears to be saved as the new item form when you click OK. However, the next time that you view the properties of the list, the New item form box is empty.
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CAUSE
This issue occurs if you deleted the List Form Web Part from the NewForm.aspx page.
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RESOLUTION
To resolve this issue, delete the list, and then re-create it. Then, customize the NewForm.aspx page. When you customize the NewForm.aspx page, make sure that you do not delete the List Form Web Part.
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MORE INFORMATION
If you want to customize the controls that appear on the NewForm.aspx page, and if you do not want to show the default List Form Web Part, you can hide the List Form Web Part. To do this, follow these steps: 1. Start SharePoint Designer 2007, and then open the NewForm.aspx page for the list.
2. Right-click the List Form Web Part, and then click Web Part Properties.
3. Expand Layout, click to select the Hidden check box, and then click OK.