Windows 10 build 17661 bugs: Install errors, Windows Security issues, and more

by Madalina Dinita
Madalina Dinita
Madalina Dinita
Windows & Software Expert
Madalina has been a Windows fan ever since she got her hands on her first Windows XP computer. She is interested in all things technology, especially emerging technologies... read more
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Windows 10 build 17661 bugs

Microsoft recently rolled out Windows 10 build 17661 to Fast Ring Insiders and Insiders who opted to Skip Ahead.

This new build introduces a series of new features that will be available on Redstone 5 – Windows 10 version 1809.

The purpose of the Windows Insider program is for user to test and code of the upcoming Windows 10 version so as to detect any major bugs.

The Redmond giant already published a list of known issues affecting the release, but as it happens with every new build, Insiders came across a bunch of new bugs.

We scoured Microsoft’s forums to identify the most common Windows 10 build 17661 problems reported by Insiders and we’ll list them below.

Windows 10 build 17661 issues

1. Install fails

Many Insiders got error 0xc1900101 when they tried to install the latest Windows 10 build. Their computers quickly reverted all the changes, and they’re now stuck on the previous build release.

I upgraded to Build 17661 today and received error 0xc1900101 and reverted back to 17134.

If you also encountered this problem, follow the instructions available in the troubleshooting guides listed below:

2. The ‘Free Up Space Now’ button is unavailable

free up space now issues
Microsoft introduced the ‘Free Up Space Now‘ option to allow users to quickly delete junk files from their computers. Unfortunately, the option is greyed out on Windows 10 build 17661, as this Insider reports:


In Settings, Storage and click on Free Up Space Now used to populate with several items to choose from for cleanup similar to Disk Cleanup. Just nothing showing now. This is still occurring in Build 17661 as it has been in the last couple Skippy Builds.

3. Windows Security doesn’t work

Microsoft also revamped the Windows Defender Security Center and named it Windows Security. It seems that this name change also brought along one minor issue — Windows Security is totally blank when users launch it for the first time. The good news is that a few restarts usually fix the problem.

OK, it does sort of populate somewhat, but nothing shows. a green check and then everything hangs, then closes. Don’t even have a title bar. Also can’t open from WU.

4. Copy doesn’t work on Edge

Using the copy function on Edge often fails on this build. The elements that users copy don’t go to the clipboard.

These are the most common Windows 10 build 17661 problems reported by Insiders. As you can, this build version is not affected by severe issues such as system freezes, crashes, BSOD errors and so on. If you already installed build 17661 on your machine, use the comments below to tell us more about your experience.


Still having issues? Fix them with this tool:


If the advices above haven't solved your issue, your PC may experience deeper Windows problems. We recommend downloading this PC Repair tool (rated Great on to easily address them. After installation, simply click the Start Scan button and then press on Repair All.

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