Getting error Content type cannot be encoded

Hello there, I have been getting an error every now and then. I am not sure why.

{"code":406,"message":"Content type cannot be encoded."}

I noticed that if I send the header of content accept to JSON it works. The strange thing is that I was successfully getting a JSON response a few days ago. What could the problem be anyone know?

This is the Url I am sending:

http://volt.utep.edu/news/index.php?option=com_api&app=articles&resource=article&category_id=36&direction=2&format=raw