Possible Cause: You've probably indexed documents written in multiple languages and encodings. Web Search can index most of the world's languages and encodings. However, Web Search needs to know the encoding of each document.
Possible Cause: Some of your documents were probably not tagged with an encoding or were incorrectly tagged.
Action: Make sure all of your documents contain the correct Content-Type META tag. If your international documents do not contain a Content-Type META tag, either add it or use the Encoding (If Not in META Tags) index definition option to specify the default encoding.