Title says it all. I saved a piece as MusicXML and imported into Sibelius. Received this:

This is not a MusicXML file and cannot be loaded. content of element kind does not match its type definition: String content is not listed in the enumeration facet.

If you need to talk to Sibelius, good luck, Avid, in its infinite greed - er, wisdom, sorry, just fired the entire programming staff.