A Strange Error In Plugin

I found a very frequent error in the log file of jboss, in which we build a plugin for openfire to run. Here is the error:

java.io.EOFException: no more data available - expected end tag </stream:stream> to close start tag <stream:stream> from line 1, parser stopped on END_TAG seen ...<query xmlns="jabber:iq:roster"/></iq>... @1:780

21:18:01,422 ERROR [stderr] (Smack Packet Reader (20))           at org.xmlpull.mxp1.MXParser.fillBuf(MXParser.java:3035)

21:18:01,422 ERROR [stderr] (Smack Packet Reader (20))           at org.xmlpull.mxp1.MXParser.more(MXParser.java:3046)

21:18:01,423 ERROR [stderr] (Smack Packet Reader (20))           at org.xmlpull.mxp1.MXParser.nextImpl(MXParser.java:1144)

21:18:01,423 ERROR [stderr] (Smack Packet Reader (20))           at org.xmlpull.mxp1.MXParser.next(MXParser.java:1093)

21:18:01,423 ERROR [stderr] (Smack Packet Reader (20))           at org.jivesoftware.smack.PacketReader.parsePackets(PacketReader.java:316)

21:18:01,424 ERROR [stderr] (Smack Packet Reader (20))           at org.jivesoftware.smack.PacketReader.access$000(PacketReader.java:46)

21:18:01,424 ERROR [stderr] (Smack Packet Reader (20))           at org.jivesoftware.smack.PacketReader$1.run(PacketReader.java:72)

because the exception occurs very frequent, almost 2 times in one second.

Is there anyone knows the likely cause? Thanks a lot.