Read more here: Why am I seeing a critical update notification?
If you get a critical or important update notification on your phone, we're letting you know that there's an important update that will fix a particular problem. We recommend that you install any critical updates immediately. Here's how a critical update works:
- If you manually check for updates, you'll be prompted at regular intervals to download the update.
- Once the update is ready to install, you'll be prompted at regular intervals to install the update.
- For mandatory updates, if you've postponed the update, it will automatically install in three days.
You may be seeing a critical or important update notification for the following reason:
We identified a problem in some versions of Windows Phone 8.1 that could cause a phone to restart periodically. A critical update will fix this problem. If you're unable to install the update or want to learn more, we can help you fix your phone.
Important: Connect to Wi-Fi, so you will have a better chance to quickly download the update. Or, make sure your cellular data connection shows 3G, 4G, or LTE. If you have a 2G or 2.5G (EDGE) connection, you’ll be prompted for updates but won’t be able to download them until you have a higher cellular data connection or connect to Wi-Fi. To learn more about the icons that appear at the top of your phone, see What do the icons on my phone mean?
To address the ongoing update failure (80188308) experienced by some HTC 8X and 8XT phones, we've stopped delivery the mandatory update to these devices. Within a few days these phones will stop prompting you to download and install the mandatory update. The vast majority of these HTC 8X and 8XT phones already applied a similar fix to the mandatory update by taking advantage of an existing 'self-healing' system component. To learn more about the situation and how to use an app to confirm your phone is OK and will not restart periodically, go to this page.
Microsoft remains committed to ensuring HTC phones have a great experience on Windows Phone, and will continue to work with HTC for future improvements and solutions to impacted phones.