In the administration backend, when adding a file to attribute of type object relations, the file upload will fail and the following error will be displayed: "Unable to parse the JSON response."
The issue seems to affect Internet Explorer only.
Steps to reproduce:
Start with a content class with an attribute of type object relations.
1. Create a new content object
2. Click the "Upload a file" button
3. Browse your filesystem and select a file to upload
4. Click the "Upload the file" button
You will get the following error (see attached screenshot):