When installing Microsoft SQL Server 2012, you may get this error:
Microsoft SQL Server 2012 Setup
The following error has occurred:
Error while enabling Windows feature: NetFx3, Error Code: -2146498298 , Please try enabling Windows feature : NetFx3 from Windows management tools and then run setup again. For more information on how to enable Windows features…
This error is caused because the Windows feature NetFx3 (which is a part of .NET Framework 3.5) isn’t enabled. SQL Server setup tries to enable the feature during installation, but fails. To fix the error, install .NET Framework (enable the Windows feature), then rerun the SQL Server 2012 setup again.
See this article for how to enable the .NET Framework 3.5 feature on Windows Server 2012 when it fails to install.