Openfire: Socket Closing session due to exception

Hello

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

Closing session due to exception: (SOCKET, R: /197.35.39.45:59545, L: /172.31.9.228:5222, S: 0.0.0.0/0.0.0.0:5222)

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: /197.135.243.195:54858, L: /172.31.9.228:5222, S: 0.0.0.0/0.0.0.0:5222)

Can you advice about that?

Thanks