Q. Why is this missing DLL file bollixing my applications?

Q. Until recently, my Win7 PC was working well with the online apps I use. Then, I could no longer access them and the system displayed: Api-Ms-Win-Runtime-|1.1.0.dll.

I tried to find it on my PC, but without success. I went to Microsoft’s site and spent about 30 minutes trying to get through to something besides Win10 offers. I finally found a reference to the missing DLL file, but the only posts were from others with the same problem.

Why is this happening and how can I keep using Windows 7?

A. The missing Api-Ms-Win-Runtime is part of Microsoft’s Universal C/C++ Run-Time (CRT), a DLL package that allows apps created with Visual C or C++ programming tools to run on any Windows system.

There used to be two, separate C run-time .dlls: AppCRT and DesktopCRT. But in July, Microsoft combined them into one library called the Universal CRT. (The package was rolled out with Windows 10.)

This change is part of the “Windows anywhere” push, which lets app makers create one version of their software that, in theory, will run on any Windows version (Vista through Win10), on desktops, tablets, or mobile systems.

The new Universal CRT is backward compatible, so that apps designed to use older DLLs should be able to use the newer ones. (For more information: See MSDN’s “Universal CRT” article.)

However, there can be trouble if the update misfired or if an app was hard-coded to use a particular instance of the earlier CRTs — or if it uses the long-discredited practice of shipping with its own copy of the CRT.

The usual solution is simply to reinstall the Universal CRT package.

If your troubles started over the summer, reinstall the original CRT package, available via Microsoft Download Center.

If your app troubles began more recently (the Universal CRT was updated in September) try downloading the update.

After the Universal CRT libraries are correctly installed, your apps should work normally again.

(Originally published on Windows Secrets on Thursday, November 5, 2015.)

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