TYPO3 Extension Error: Cannot create empty instance of the class -

My FE plugin, created using the extension builder, shows me the following error:

  Can not create empty Example of the class "TYPO3 \ CMS \ Extbase \ Persistence \ ObjectStorage" because it does not apply TYPO3 \ CMS \ Extbase \ DomainObject \ DomainObjectInterface.   
 What does this mean and how do I resolve it? TYPO3 version 6.1.0  
 is related to my domain object named  subject   Category_Id m: n relation  and  Location_ID 1: n connection  code> I did not map these two in any table.  
 How can I tell in detail how this relation relates to some tables ( class_table and location_table ) and to get data being viewed in their respective domain model objects Are you  
 The problem is a little misleading, I hope I made myself clear  
 thanks   
 
 
 You need to establish relationships within the  TCA .  
 Clear the cache and  typo3temp / cache / .  
 Then you will  need to annotate your model  properly that  can extbase  solve the reference.  
 Remember: Annotation for the  TCA  and  extbase     for the core