why am i getting these errors?

I would really appreciate it if someone can tell me why I'm getting the
following errors with an embedded resource when it is requested by jmeter.
The error is in response to a request for .css and in another sampler a
.js. And it happens intermittently, not consistently. The number of threads
is only 5 and loop count is 50.
My samplers are set to retrieve the embedded resources with a pool size of
8. I have added a cache manager and I'm clearing the cache for each
iteration.

Is the connection timing out or is it because of the firewall or could it
be some other reason?

Regards
Sam

org.apache.http.conn.
ConnectTimeoutException: Connect to xxxxxxxxx timed out at
org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:551)
at
org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180)
at
org.apache.http.impl.conn.ManagedClientConnectionImpl.open(ManagedClientConnectionImpl.java:294)
at
org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:645)
at
org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:480)
at
org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:906)
at
org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:805)
at
org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.sample(HTTPHC4Impl.java:286)
at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerProxy.sample(HTTPSamplerProxy.java:62)
at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase$ASyncSample.call(HTTPSamplerBase.java:1804)
at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase$ASyncSample.call(HTTPSamplerBase.java:1772)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source) at
java.util.concurrent.FutureTask.run(Unknown Source) at
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase$1$1.run(HTTPSamplerBase.java:1240)
at java.lang.Thread.run(Unknown Source)

org.apache.http.conn.HttpHostConnectException: Connection to xxxxxx refused
at
org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:190)
at
org.apache.http.impl.conn.ManagedClientConnectionImpl.open(ManagedClientConnectionImpl.java:294)
at
org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:645)
at
org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:480)
at
org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:906)
at
org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:805)
at
org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.sample(HTTPHC4Impl.java:286)
at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerProxy.sample(HTTPSamplerProxy.java:62)
at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase$ASyncSample.call(HTTPSamplerBase.java:1804)
at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase$ASyncSample.call(HTTPSamplerBase.java:1772)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source) at
java.util.concurrent.FutureTask.run(Unknown Source) at
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at
org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase$1$1.run(HTTPSamplerBase.java:1240)
at java.lang.Thread.run(Unknown Source) Caused by:
java.net.ConnectException: Connection timed out: connect at
java.net.DualStackPlainSocketImpl.waitForConnect(Native Method) at
java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source) at
java.net.AbstractPlainSocketImpl.doConnect(Unknown Source) at
java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source) at
java.net.AbstractPlainSocketImpl.connect(Unknown Source) at
java.net.PlainSocketImpl.connect(Unknown Source) at
java.net.SocksSocketImpl.connect(Unknown Source) at
java.net.Socket.connect(Unknown Source) at
sun.security.ssl.SSLSocketImpl.connect(Unknown Source) at
org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:549)
at
org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180)
... 15 more