Blog de Eduardo Osorio Armenta

The meta:progid attribute on the Page directive is necessary if the page will ever be opened in SharePoint Designer. You should include this as site pages are supposed to support customization and thus, be opened in SharePoint Designer. If you don't want to allow pages to be opened and customized in SharePoint Designer, then you should do that through permissions, not at the page level. Using ASP.NET 2.0 Code Behind Files in SharePoint v3 Sites SPFile.ProgID gets a string that identifies the application in which the file was created. That's all the meta:progid is about. It's a identifier for SharePoint and you probably should not use other attributes, they might cause run-time error. Ref: msdn forum thread explanation

Office SharePoint Designer microsoft documentation Renaming Web Application Content Database Database that support SharePoint 2010 Products (poster)

apply all this Microsoft:  Error message when you try to attach a file in a custom form on the Web site in Windows SharePoint Services 3.0: “This form was customized not working with attachement" Blog:  Custom listview with attachments sharepoint designer hotfix http://support.microsoft.com/kb/960311 not sure if Office 2007 SP2 must contain that hotfix. Setting SharePoint Form Fields Using Query String Variables Without Using JavaScript Understanding SharePoint’s “ddwrt:DataBind” syntax Customise SharePoint List Forms MSDN: List Forms ListTemplates Elements (features schemas) Tools for CAML intellisense: CAML.NET IntelliSense jPoint