ClassCircularityError is thrown when getCanonicalName

Exception stacks.

Exception in thread "main" java.lang.ClassCircularityError: 
plugins/agents/Agent
        at java.lang.Class.getDeclaringClass(Native Method)
        at java.lang.Class.getEnclosingClass(Class.java:1085)
        at java.lang.Class.getCanonicalName(Class.java:1169)
        at agents.loader.AgentLoader.getPluginAgentFromCache(AgentLoader.java:288)
        at compiler.AgentCompiler.main(AgentCompiler.java:365)

Below is the code which cause the error. It's very strange if I change the getCanonicalName to getName then everything is fine. These loaded classes are loaded with customized ClassLoader. like cl = defineClass(name, byteArray, 0, byteArray.length);

public Class getPluginAgentFromCache(String name)
{
    if (_loadedClasses == null)
        return null;

    Iterator <Class> iter = _loadedClasses.iterator();

    while (iter.hasNext())
    {
        Class c=iter.next(); 
        if (c.getCanonicalName().equals(name))
            return c;
    }

    return null;        
}

Any one can tell me why getCanonicalName here will throw this error? (JDK 1.6.0_20)

UPDATE After some research, I find that when you define the class you must load the its parent class first. But it's hard. When I write to the binary, they are just ordered by the sequence in the file folder. So when I load them, they will not order by the class hieriarchy. It's a bit annoying here.For now I just loop the classes , then load the error class again. This is workaround but not a good one.