Share 'What is ning.xauth.client.exceptions.ClientException?'

I developed a Ning application on my network, that worked nicely until yesterday. Unfortunately, today I received a couple of times the following error message, from a simple call to the Ning API: {"success":false,"reason":"An unexpected ClientException (ning.xauth.client.exceptions.ClientException) occurred: Unknown IO exception occurred","status":500,"code":1,"subcode":0,"trace":"7f356a60-8ff4-…