Web Part Error: Unknown server tag 'wpns1:PortalDVCThongBaoKhuyenMai'.

Error Details:
[HttpParseException: Unknown server tag 'wpns1:PortalDVCThongBaoKhuyenMai'.]
  at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding)
  at System.Web.UI.TemplateParser.Parse()
  at System.Web.UI.DesignTimeTemplateParser.ParseControlsInternal(DesignTimeParseData data, Boolean returnFirst)
  at System.Web.UI.DesignTimeTemplateParser.ParseControl(DesignTimeParseData data)
  at System.Web.UI.Design.ControlSerializer.DeserializeControlInternal(String text, IDesignerHost host, Boolean applyTheme)
  at System.Web.UI.Design.ControlParser.ParseControl(IDesignerHost designerHost, String controlText)
  at Microsoft.Web.Design.Server.ServerDocument.Microsoft.Web.Design.Server.IServerDocumentDesigner.ParseControl(String outerHtml)
  at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CompressUsingMicrosoftWebDesigner(SourceContent sourceContent, String allRegisterDirectives)
  at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CompressInOrder(Deserializer firstMethod, Deserializer secondMethod, SourceContent sourceContent, String allRegisterDirectives, Boolean isClosed)

[HttpParseException: Unknown server tag 'wpns1:PortalDVCThongBaoKhuyenMai'.]
  at System.Web.UI.TemplateParser.ProcessException(Exception ex)
  at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding)
  at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding)

[HttpException: Unknown server tag 'wpns1:PortalDVCThongBaoKhuyenMai'.]
  at System.Web.UI.TagPrefixTagNameToTypeMapper.System.Web.UI.ITagNameToTypeMapper.GetControlType(String tagName, IDictionary attribs)
  at System.Web.UI.MainTagNameToTypeMapper.GetControlType2(String tagName, IDictionary attribs, Boolean fAllowHtmlTags)
  at System.Web.UI.MainTagNameToTypeMapper.GetControlType(String tagName, IDictionary attribs, Boolean fAllowHtmlTags)
  at System.Web.UI.RootBuilder.GetChildControlType(String tagName, IDictionary attribs)
  at System.Web.UI.ControlBuilder.CreateChildBuilder(String filter, String tagName, IDictionary attribs, TemplateParser parser, ControlBuilder parentBuilder, String id, Int32 line, VirtualPath virtualPath, Type& childType, Boolean defaultProperty)
  at System.Web.UI.TemplateParser.ProcessBeginTag(Match match, String inputText)
  at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding)