How do I deal with kafka-avro-console-producer fails? - kafka-producer-api

Question

When followed the confluent platform quickstart, I got stuck in step 5. An error occured:
[root#CentOS-70 confluent-3.1.2]# ./bin/kafka-avro-console-producer --broker-list localhost:9092 --topic mytopic --property value.schema='{"type":"record","name":"myrecord","fields":[{"name":"f1","type":"string"}]}'
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/home/wei_liu/confluent-3.1.2/share/java/kafka-serde-tools/slf4j-log4j12-1.7.6.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/home/wei_liu/confluent-3.1.2/share/java/schema-registry/slf4j-log4j12-1.7.6.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]
{"f1": "value1"}
org.apache.kafka.common.errors.SerializationException: Error registering Avro schema: {"type":"record","name":"myrecord","fields":[{"name":"f1","type":"string"}]}
Caused by: io.confluent.kafka.schemaregistry.client.rest.exceptions.RestClientException: Register schema operation failed while writing to the Kafka store; error code: 50001
at io.confluent.kafka.schemaregistry.client.rest.RestService.sendHttpRequest(RestService.java:170)
at io.confluent.kafka.schemaregistry.client.rest.RestService.httpRequest(RestService.java:187)
at io.confluent.kafka.schemaregistry.client.rest.RestService.registerSchema(RestService.java:238)
at io.confluent.kafka.schemaregistry.client.rest.RestService.registerSchema(RestService.java:230)
at io.confluent.kafka.schemaregistry.client.rest.RestService.registerSchema(RestService.java:225)
at io.confluent.kafka.schemaregistry.client.CachedSchemaRegistryClient.registerAndGetId(CachedSchemaRegistryClient.java:59)
at io.confluent.kafka.schemaregistry.client.CachedSchemaRegistryClient.register(CachedSchemaRegistryClient.java:91)
at io.confluent.kafka.serializers.AbstractKafkaAvroSerializer.serializeImpl(AbstractKafkaAvroSerializer.java:72)
at io.confluent.kafka.formatter.AvroMessageReader.readMessage(AvroMessageReader.java:158)
at kafka.tools.ConsoleProducer$.main(ConsoleProducer.scala:55)
at kafka.tools.ConsoleProducer.main(ConsoleProducer.scala)