Openfire: Socket Closing session due to exception


I checked errors and warnings of my openfire server and found many errors like that:

Closing session due to exception: (SOCKET, R: /, L: /, S:

org.apache.mina.filter.codec.ProtocolDecoderException: org.jivesoftware.openfire.nio.XMLNotWellFormedException: Character is invalid in: (Hexdump: 17 03 01…

2015.01.20 19:51:48 org.jivesoftware.openfire.nio.ConnectionHandler - ConnectionHandler reports IOException for session: (SOCKET, R: /, L: /, S:

Can you advice about that?