Weird thing happened to my GData application – it started throwing “Unable to readresponse, or response is empty” error on upload. The only thing to matter seemed to be a file size.
After some time of serching the Internet found the solution – try to increase timeout limit in Zend/Htt/client.php script. It set to 10 seconds by default. I changed to 20 and it solved the problem.
Hope it will help someone too!