What is meaning of "class is not assignable"?

I'm using Eclipse Helios, JSF 2 and Glassfish 3.1 server..... and what's happen error like that ...

javax.servlet.ServletException: com.sun.faces.mgbean.ManagedBeanCreationException: Unable to create managed bean contactController.  The following problems were found:
     - The property groupRepository for managed bean contactController is defined with a property class of ibm.contact.model.ContactRepository, however, this class is not assignable to the property.

What 开发者_Python百科is meaning of that error and how to fix it ?

I can just try to guess. Your property groupRepository on controller ContactController is of different type then the instance that the container is trying to inject into this property so its not asignable. Are you injecting it trough some interface? Is the type of property groupRepository in your controller interface?