Microsoft is rolling out an update that removes .NET 3.5 from Windows 10 PC’s
Unfortunately Graphical CounterAct requires .NET 3.5 to run.
The easiest solution is just to reinstall .NET 3.5 from the Microsoft Website.
Click on the link below and follow the steps to install https://www.microsoft.com/en-gb/download/details.aspx?id=21
Hopefully further updates will not remove it again.