The Ribbon Tab with id: "Ribbon.Read" has not been made available for this page or does not exist. Use Ribbon.MakeTabAvailable(). at Microsoft.Web.CommandUI.Ribbon.Render(HtmlTextWriter writer) at Microsoft.SharePoint.WebControls.SPRibbon.Render(HtmlTextWriter writer)

Add this code in the webpart:

 

Page currentPage = this.Page;

SPRibbon ribbon = SPRibbon.GetCurrent(this.Page);

SPContext context = SPContext.Current;

ribbon.MakeTabAvailable(SPRibbon.ReadTabId);

 

Add the Windows.Web.CommandUI dll reference.

 

Enjoy.