Hi,
This may be because someone had enhanced the view and then delete the enhancement, but the classes may not be deleted which causes the Error.
Please check in SE80 under your package and check is there exist any classes created for the view , because when we enhance the view the system automatically creates the classes with its own namespace ( e.g. start with Z etc) as shown below. If the classes are there then you need to delete those classes and then try again to Enhance your class.
Thanks
Kumar Gaurav.