I had the same problem getting Symantec EndPoint protection v11.0 running on some machines on our network and we learned that we only saw the problem on multicore processor machines running Symantec Endpoint Protection beginning with version 11.0.5x. The last good version is 11.0.4x. Symantec said the problem will be fixed with the next maintenance pack. Once we downgraded to version 11.0.4x we did not have the problem again.