尝试通过openjpa连接到derby服务器时出现以下异常：
attempted duplicate class definition for name: "sun/security/pkcs11/SunPKCS11"。通过一些谷歌搜索结果，它看起来像是mac上java的已知问题，但我使用的是ubuntu和openjdk-6。我真的不知道从哪里开始解决这个问题。任何想法都出错了？
java -version输出：
java version "1.6.0_24"
OpenJDK Runtime Environment (IcedTea6 1.11.1) (6b24-1.11.1-4ubuntu3)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)
错误堆栈跟踪（冗长...）
Exception in thread "main" <openjpa-2.2.0-r422266:1244990 nonfatal general error> org.apache.openjpa.persistence.PersistenceException: There were errors initializing your configuration: java.lang.LinkageError: loader (instance of sun/misc/Launcher$ExtClassLoader): attempted duplicate class definition for name: "sun/security/pkcs11/SunPKCS11"
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at java.lang.ClassLoader.loadClass(ClassLoader.java:314)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
at sun.security.jca.ProviderConfig$3.run(ProviderConfig.java:253)
at sun.security.jca.ProviderConfig$3.run(ProviderConfig.java:244)
at java.security.AccessController.doPrivileged(Native Method)
at sun.security.jca.ProviderConfig.doLoadProvider(ProviderConfig.java:244)
at sun.security.jca.ProviderConfig.getProvider(ProviderConfig.java:224)
at sun.security.jca.ProviderList.loadAll(ProviderList.java:281)
at sun.security.jca.ProviderList.removeInvalid(ProviderList.java:298)
at sun.security.jca.Providers.getFullProviderList(Providers.java:170)
at java.security.Security.getProviders(Security.java:457)
at java.security.Security.getProviders(Security.java:607)
at java.security.Security.getProviders(Security.java:552)
at org.apache.derby.client.am.EncryptionManager.<init>(Unknown Source)
at org.apache.derby.jdbc.ClientBaseDataSource.<clinit>(Unknown Source)
at org.apache.derby.jdbc.ClientDriver.tokenizeURLProperties(Unknown Source)
at org.apache.derby.jdbc.ClientDriver.connect(Unknown Source)
at org.apache.commons.dbcp.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:38)
at org.apache.commons.dbcp.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:582)
at org.apache.commons.dbcp.BasicDataSource.validateConnectionFactory(BasicDataSource.java:1556)
at org.apache.commons.dbcp.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:1545)
at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1388)
at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
at org.apache.openjpa.jdbc.schema.DBCPDriverDataSource.getDBCPConnection(DBCPDriverDataSource.java:74)
at org.apache.openjpa.jdbc.schema.AutoDriverDataSource.getConnection(AutoDriverDataSource.java:42)
at org.apache.openjpa.jdbc.schema.SimpleDriverDataSource.getConnection(SimpleDriverDataSource.java:75)
at org.apache.openjpa.lib.jdbc.DelegatingDataSource.getConnection(DelegatingDataSource.java:118)
at org.apache.openjpa.lib.jdbc.DecoratingDataSource.getConnection(DecoratingDataSource.java:93)
at org.apache.openjpa.jdbc.schema.DataSourceFactory.installDBDictionary(DataSourceFactory.java:233)
at org.apache.openjpa.jdbc.conf.JDBCConfigurationImpl.getConnectionFactory(JDBCConfigurationImpl.java:733)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.apache.openjpa.lib.conf.ConfigurationImpl.instantiateAll(ConfigurationImpl.java:295)
at org.apache.openjpa.conf.OpenJPAConfigurationImpl.instantiateAll(OpenJPAConfigurationImpl.java:1671)
at org.apache.openjpa.kernel.AbstractBrokerFactory.makeReadOnly(AbstractBrokerFactory.java:646)
at org.apache.openjpa.kernel.AbstractBrokerFactory.newBroker(AbstractBrokerFactory.java:203)
at org.apache.openjpa.kernel.DelegatingBrokerFactory.newBroker(DelegatingBrokerFactory.java:156)
at org.apache.openjpa.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:227)
at org.apache.openjpa.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:154)
at org.apache.openjpa.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:60)
at org.dynamosoftware.jpatest.App.main(App.java:15)