Web Part Page Maintenance
In the Microsoft Knowledge Base article
830342, entitled
"Soap:Server Exception of Type Microsoft.SharePoint.SoapServer.SoapServerException" Message Appears When You Try to Edit a Portal by Using FrontPage there are a variety of solutions which probably do work. However, one of the solutions mentions opening up the web part page maintenance page.
In order to do this, simply append "?contents=1" to the URL of the page. For example:
http://myportal/myarea/default.aspx?contents=1