soap:ServerServer was unable to process request. —> A Web Part or Web Form Control on this Web Part Page cannot be displayed or imported because it is not registered as safe on this site. You may not be able to open this page in an HTML editor that is compatible with Microsoft Windows SharePoint Services, such as Microsoft Office SharePoint Designer. To fix this page, contact the site administrator to have the Web Part or Web Form Control configured as safe. You can also remove the Web Part or Web Form Control from the page by using the Web Parts Maintenance Page. If you have the necessary permissions, you can use this page to disable Web Parts temporarily or remove personal settings. For more information, contact your site administrator.

Here’s the solution that helped me to solve the issue. Original article is found here.

Under the account of a user that has rights (usually the admin account), go to the URL and add "contents=1" to it.  This will list all web parts that have been added at any particular point.

If you have a web part that you added at one point and deleted it through the URL, it still ‘exists’ and so if it wasn’t a safe part, or is no longer listed in the web.config as a safe part, it will be listed as an ‘Error’ web part.  Select it/them and delete them, and then you should be able to open the page in SharePoint Designer as expected.

For example, if you try to open the page like this: http://somehost/default.aspx?contents=1 or like this http://somehost/?contents=1 you will see the “Web Part Page Maintenance: default” and the list of currently loaded Web Parts. Check the list of Web Parts for an Error Web Part and delete it.

You can find a lot more information in The SharePoint Designer Team site including:

a) Letter to our Customers
b) Frequently Asked Questions
c) Free Download

Also, make sure to watch this video where Tom Rizzo and J.R. Arredondo discuss these changes and provide some insights into what is coming in the future (pick the appropriate version for your bandwidth).

· Small size video (6MB)
· Medium size video (17 MB)
· Large size video (83 MB)

Others who downloaded SharePoint Designer 2007 also downloaded:

1. Microsoft Office SharePoint Designer 2007 Service Pack 1 (SP1)
2. Office SharePoint Designer 2007 Training Standalone Edition
3. Windows SharePoint Services 3.0 Application Templates: All Templates
4. Windows SharePoint Services 3.0 Sample: Example Master Pages
5. Windows SharePoint Services 3.0 Tools: Visual Studio 2008 Extensions, Version 1.2