Earlier today, Microsoft released Windows 10 for PCs Insider Preview build 16288 to the Fast ring, bringing a range of changes, improvements, and fixes to the OS. Unfortunately though, upon attempting to install it, many users were getting an error message that said that their PC is installing an update with an option to retry.
If it's not entirely obvious, clicking Retry would present the exact same message again.
Microsoft quickly announced that it was aware of the issue, and it is now saying that it has been fixed. There should be new builds published, but it may take up to two hours for all variants to be made available. In other words, if you're still experiencing the issue, go grab a cup of coffee.
The Windows 10 Fall Creators Update is slated to be available to the general public on October 17; however, today's build marks the build number as 1709, which means that an RTM build should be available to Insiders sometime this month.