After you upgrade to Windows 8.1, Windows RT 8.1, or Windows Server 2012 R2, you may encounter some performance issues for applications that use the Microsoft .NET Framework.
These issues occur because some Native Image Generator (NGen) registry entries are lost during the Windows 8.1 upgrade. This causes the application native images to become invalid after the upgrade.
The .NET assemblies are precompiled to native code by NGen to improve performance. Because these native images are no longer valid after the upgrade to Windows 8.1, performance may be affected until the native images are regenerated.
If you choose not to install dynamic updates during the setup process, you can still repair or re-install any applications that are affected by this issue in order to regenerate the correct native images.
How to obtain this update
This is a dynamic update that is automatically applied when you upgrade to Windows 8.1, Windows RT 8.1, or Windows Server 2012 R2. No interaction is required to apply this update.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates
Third-party information disclaimer
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.