Gmail Gadget Error 406 being thrown on osapi.http.post

We have multiple marketplace Apps that use Gmail Contextual Gadgets. These have been ruing for years successfully.

We are now noticing the following error being thrown when calling out to an exteal web server using open social osapi.http.post

"{"id":"http.post","error":{"message":"Response not valid JSON","code":406}}"

We have checked and there is nothing wrong with our server. We can make the call directly to our server successfully without fail.

We can replicate the issue calling to multiple servers ruing different apps/gadgets. The only commonality appears to be the use of osapi.http.post.

Here is the post

          osapi.http.post({
              'body': postdata,
              'href': serverUrl + 'iLinkStreamer.ashx?data=' + "" + setTimeStamp() + debugString,
              'format': 'json',
              'authz': 'signed',
              'noCache': true
            }).execute(displayStreamList); 

which raises the 406 error as above

Has anybody else noticed this issue?? Not sure how we can address it?