ServerConnectivityException: Pool unexpected socket timed out on client connection

seeing this error on one of our gemfire clients

1. com.gemstone.gemfire.cache.client.ServerConnectivityException: Pool unexpected socket timed out on client connection=Pooled Connection to xxx.xxxxxx.com:40404: Connection[xxxxxxxxxxx.com:40404]@1325707290 attempt=2). Server unreachable: could not connect after 2 attempts

using Gemfire 6.6.3

jdk:     java version "1.6.0_22"

Looks like the socket closed unexpectedly on the client. The locator and server processes were up and running there was no outage. Is there a client socket timeout setting that can prevent this? What can cause this?

Thanks