Deserializing issue with Spring Data Redis with Lettuce

Environmnet:
aix 7.1
redis 2.6.17
jdk 1.6
spring-data-commons-1.12.11.RELEASE
spring-data-keyvalue-1.1.11.RELEASE
spring-data-redis-1.7.11
lettuce-3.5.0.Final
A Redis server running on the same host with web applications (clients to Redis)

The problem:
I have set the following RedisTemplate Bean configuration:

@Beanpublic RedisTemplate<String, Object> redisTemplate() {    RedisTemplate<String, Object> redisTemplate = new RedisTemplate<String, Object>();    redisTemplate.setConnectionFactory(redisConnectionFactory());    redisTemplate.setEnableTransactionSupport(true);    redisTemplate.setKeySerializer(new StringRedisSerializer());    redisTemplate.sethashKeySerializer(new StringRedisSerializer);    return redisTemplate;}

and also the following is a code of a validation checker for a Redis server:

public class ObservableRedisStateChecker implements Runnable {    ...    public void run() {       try {           Thread.sleep(3000);           redisTemplate.opfForValue().get("validation");           notifyObservers(true);       } catch (Exception e) {           noifyObservers(false);  // meaning that the Redis' state isn't fine.       }    ...}

The above ObservableRedisStateChecker checks periodically and notify other instances the state of the Redis server. The code usually works fine, but when too many requests are made, the following error occurs:

org.springframework.data.redis.serializer.SerializationException: Cannot deserialize; nested exception is org.springframework.core.serializer.support.SerializationFailedException: Failed to deserialize payload. Is the byte array a result of corresponding serialization for DefaultDeserializer?; nested exception is java.io.EOFException

A weird point is that when I launch a simple test application which runs a very same code with the above validation code on the same host the error occurs, while the error is occurring, the test application says no error. the error is just occurred on the web applications.
The test code is as follows:

...ExecutorService es = Executors.newCachedThreadPool()RedisTemplate<String, Obejct> redisTemplate = ...es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));es.submit(new RedisValidationCheckTest(redisTemplate));...

What's wrong with it?