JSON API only GET is working

Hello there

I am currently playing arround with the JSON API and so far i can query various things flawlessly. However, as soon as i try to set, add or update i get an error message:

{
  "result": [
    {
      "url": "/dvmdb/adom/xxx/script/",
      "status": {
        "message": "No permission for the resource",
        "code": -11
      }
    }
  ],
  "id": 1

rpc permissions for user is set to read/write, also user is member of the superuser group.

Can anyone give a hint where this problem is coming from?

Thanks in advance

Petr