If you were using Geta.EPi.ShellRazorSupport library, uninstall it and upgrade your module project to the latest version (Episerver.CMS.UI 10.10.2 or later). Then open your module.config file and an attribute viewEngine on the module tag. There are three available values for the viewEngine attribute - None, Razor, and WebForm.
module.config for Razor support would look like this:
<?xml version="1.0" encoding="utf-8"?> <module viewEngine="Razor"> <assemblies> <add assembly="MyModule" /> </assemblies> </module>
If you were using Geta.EPi.ShellRazorSupport you also should notify your module users to uninstall it. Add some upgrade notes to your package readme.txt or do it differently.