Web Part Error: Unknown server tag.
Error Details:
[WebPartPageUserException: Unknown server tag.]
at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CompressInOrder(Deserializer firstMethod, Deserializer secondMethod, SourceContent sourceContent, String allRegisterDirectives, Boolean isClosed)
at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CompressWebPartNoSave(Boolean isClosed)