Setup - Create an Object Relations class

1.Login as admin on administration interface
2.Click in Setup tab on top menu
3.Click in Classes on left menu
4.Click in Content on Class Group block
5.Click in New Class button
  Name : Object relations
  Identifier : object_relations
  Object name pattern : <name>
  Attribute (Text line) :
  Name : Name
  Identifier : name
  Attribute ( Object relations )
  Name : Object relations
  Identifier : object_relations
6. Click in OK button

Setup - Upload an image

1. Click in Content Structure tab on top menu 
2. Create an Object Relation
    Name: Relation object
3. Click in Add objects button
4. Check the box near News
5. Click in Select button
6. Click in Add objects button
7. Check the box near Knowledge
8. Click in Select button
9. Click in Upload a file button
10.Select an image file from your computer
11. Click in Upload file button

Pop-up with the following error.

Unable to parse the JSON response