When programatically adding a form to a placeholder (as described in the "WFFM Reference Guide" on the SDN website), the form may not show the expected submit action messages.
For example, verification, save action error, or validation messages may not be displayed.
Modify the code that you used to add the form using the line in
bold:
Sitecore.Form.Core.Renderings.FormRender fr = new Sitecore.Form.Core.Renderings.FormRender();
fr.FormID = "BF308460-1184-490C-98C6-2EE7DEC5C819";//form item id
fr.FormTemplate = "/sitecore modules/web/Web Forms for Marketers/Control/SitecoreSimpleFormAscx.ascx";
Sitecore.Context.Page.GetPlaceholder("content").Controls.Add(fr);