3396695 - SAP PI OAuth - Receiver Rest Adapter/Access token request error

OAuth access token fetch isn't working. 
Error while processing Authorization request!
[EXCEPTION]
com.sap.aii.af.sdk.xi.oauth.json.JSONException: A JSONObject text must begin with '{' at 1 [character 2 line 1]

In the HTTP traces you can find the response of the access token request similar to the bellow:

HTTP_CLIENT : 757 REPLY: 
3cd.....{"access_token":"xxxxxxxxxxxxxx","token_type":"BEARER","expires_in":3600,"scope":"yyyyyyyyyy"}..0..

SAP Netweaver 7.5

PI/PO

KBA , BC-XI-CON-RST , Rest Adapter , Problem