Web Part Error: The file you imported is not valid. Verify that the file is a Web Part description file (*.webpart or *.dwp) and that it contains well-formed XML.

Error Details:
[WebPartPageUserException: The file you imported is not valid. Verify that the file is a Web Part description file (*.webpart or *.dwp) and that it contains well-formed XML.]
  at Microsoft.SharePoint.WebPartPages.WebPartImporter.CreateXdoc(XmlReader reader)
  at Microsoft.SharePoint.WebPartPages.WebPartImporter..ctor(SPWebPartManager manager, XmlReader reader, Uri webPartPageUri, SPWeb spWeb)
  at Microsoft.SharePoint.WebPartPages.WebPartImporter..ctor(SPWebPartManager manager, XmlReader reader, Assembly assembly, String typeName, SPWeb spWeb)
  at Microsoft.SharePoint.WebPartPages.WebPartImporter.ImportFromNamespace(SPWebPartManager manager, String webPartXml, Boolean clearConnections, Type type, SPWeb spWeb)
  at Microsoft.SharePoint.WebPartPages.WebPartTagReader.ParseWebPartTag()
  at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CompressUsingXmlDeserializer(SourceContent sourceContent)
  at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CompressInOrder(Deserializer firstMethod, Deserializer secondMethod, SourceContent sourceContent, String allRegisterDirectives, Boolean isClosed)