Sorry about that... ContainerName is either LeftPane, ContentPane, or RightPane. The FreeForm class extends ContentData, and only adds one additional property called “Html”. Sorry about not specifying that earlier!And yes, the PageID is the same as TabID you see in the browser address bar. Makes it possible to move the content around if you want to.
Error: Server was unable to process request. --> Invalid login for publishing the specified content, or the content instance specified does not exist!