The Microsoft .NET Framework January 2018 Security and Quality Rollup that was released on January 9, 2018 contains a big mistake that causes any calls to Fonts.SystemFontFamilies to immediately throw an exception.
This affects some of our UI control products, many other third party apps, and possibly your own code as well since that API is a commonly-used .NET property.
The problem doesn't seem to occur on Windows 10, but does occur on Windows 7 systems that have installed the rollup.
The exception message that appears is something like:
No FontFamily element found in FontFamilyCollection that matches current OS or greater: Windows7SP1
With stack trace:
The only workaround at the moment until it is fixed by Microsoft appears to be to uninstall the KB4055532 rollup on Windows 7 machines.
We expect this to be resolved by Microsoft quickly since posts about it are popping up all over the Internet:
Update: Official thread from Microsoft acknowledging it and providing a temporary workaround (thanks Stéphane):
Update 2: Microsoft appears to have released an updated patch that should resolve the fonts issue.