Spark client closes for no apparent reason. The end user sees msg: "Your connection was closed due to an error"

Spark client closes for no apparent reason. The end user sees msg: "Your connection was closed due to an error"

I looked at the logs and saw this error message that occurred at the time of one of my end users having this problem.

this is the error that i'm seeing:

1. 2015.08.13 13:29:56 org.jivesoftware.openfire.nio.ConnectionHandler - Closing connection due to exception in session: (0x000001AA: nio socket, server,......................

and this:

          2.   2015.08.13 13:29:56 org.jivesoftware.openfire.nio.OfflinePacketDeliverer - Could not route packet

wondering if this has something to do with java. . .

this only seems to be happening with a few or handful users. I turned on debugging.