用Proguard处理后的ClassNotFoundException

如何解决用Proguard处理后的ClassNotFoundException

使用proguarg处理jar后，出现此异常。 Proguard设置是标准配置。可能是什么原因？当我用原始的jar替换jar时，没有错误。

java.lang.classNotFoundException: main.Key
        at java.net.urlclassloader.findClass(UnkNown Source)
        at java.lang.classLoader.loadClass(UnkNown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(UnkNown Source)
        at java.lang.classLoader.loadClass(UnkNown Source)
        at java.lang.class.forName0(Native Method)
        at java.lang.class.forName(UnkNown Source)
        at java.io.ObjectInputStream.resolveClass(UnkNown Source)
        at java.io.ObjectInputStream.readNonProxyDesc(UnkNown Source)
        at java.io.ObjectInputStream.readClassDesc(UnkNown Source)
        at java.io.ObjectInputStream.readOrdinaryObject(UnkNown Source)
        at java.io.ObjectInputStream.readobject0(UnkNown Source)
        at java.io.ObjectInputStream.readobject(UnkNown Source)
        at java.io.ObjectInputStream.readobject(UnkNown Source)
        at main.a.a(UnkNown Source)
        at main.a.a(UnkNown Source)
        at main.EntryPoint.a(UnkNown Source)
        at main.EntryPoint.main(UnkNown Source)