For several days now, owners of the Google Chromecast (2nd Gen) and the Chromecast Audio haven’t been able to use the devices. Google has finally acknowledged the issue, sending out emails to those with affected devices.
Starting around March 9th, users began reporting that they were unable to cast to their Chromecast (2nd gen) and Chromecast Audio devices. The problem shows up as an “Untrusted Device” error message that appears in apps when you try to cast video or audio.
Typically, when we see a bug like this show up, it’s only affecting a portion of users. However, this seems to be happening to all owners of the Chromecast (2nd Gen) and Chromecast Audio. That’s a very large user base, and this error has been ongoing for a few days already.
The good news is that Google is aware of the problem and is working on a fix. Owners of the devices received this email today (March 12th):
We’re contacting you because of a disruption affecting Chromecast (2nd gen) and Chromecast Audio devices. We apologize for the issue and understand your frustration. We are working to roll out a fix as soon as possible and will share updates and guidance on the Nest Community page. We appreciate your patience as we resolve this issue.
Prior to the email above, on March 10th, Google said it was “aware of an issue” with the Chromecast (2nd Gen) and Chromecast Audio and was working on a fix. The following day, Google sent out another update on the situation.
Please do not factory reset your device. If you previously performed a factory reset during troubleshooting, you may also be experiencing an issue where you’re unable to re-setup your device. The team has identified the cause for this as well and is currently working on a fix.
We’re working to resolve this as soon as possible, and will keep you updated when there is more to share.
We sincerely apologize for the inconvenience, and appreciate your patience in the meantime.
If you’re experiencing this issue, the bolded part of that statement is important. Factory resetting the device may bring on even more problems for you. For now, the only thing you can do is wait for Google to roll out a fix. There’s no specific timeline for the fix yet, but hopefully, it won’t be too long before you can cast to your Chromecast again.
One thing to note is we’re not talking about the confusingly named Chromecast with Google TV devices. Google has already discontinued that product line in most countries as of a few weeks ago. This issue is specifically tied to the Chromecast (2nd Gen) and Chromecast Audio, which rely entirely on casting content from your phone.
Keep an eye on your device, and make sure it’s connected to the internet so it can receive the update when it’s available. In the meantime, you’ll just have to find other ways to enjoy your favorite audio and video content.
Source: 9to5Google, The Verge

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