I had been unable to cast from any of my Windows 10 PC’s to either of my two Chromecasts for at least a week. I have a first gen limited to 2.4 MH spectrum, and the newer dual channel device. I went down the rabbit hole and checked the list of Google’s support FAQ’s. Network discovery, rebooting the device you name it. Nothing worked. For a moment, I even considered adding my Xfinity connection as a suspect but quickly ruled that out as I had not changed anything recently. I also noted that I had several failed Windows 10 updates. My conclusion was that the problem could be with Google’s Chrome Browser and Windows 10.
After a week of pulling out my hair, I got on the phone with a Google support agent. I gave her a rundown of the problems and my efforts to troubleshoot them and told her I 
had just updated Chrome yesterday but felt that it was a Chrome bug. While on the phone, Google started updating itself to version Chrome Update 50.3029.81 64bit. Eureka. Game over. Problem solved. If you are having problems casting Google Chrome’s auto update should be fixing it shortly.
Howard Sobel
Computing Pro Weekly Byte 