Assume that you have installed Microsoft .NET Framework 4.7. When you try to open Sitefinity based web applications, you may notice that they no longer work and throw an exception System.TypeInitializationException. Additionally, you may receive an error message that resembles the following:
This problem occurs when there's a complex nested Sitefinity custom membership provider integration. This causes the applications to break and raise the exception. Until now, there have been issues that are related to Sitefinity based ASP.NET web applications only, and we are not aware of any other ASP.NET applications that face similar issues.
To fix this issue, install the Sitefinity hotfix and redeploy it:
Note We expect to release a fix for the .NET Framework 4.7 in future for this issue as well.
For more information about known issues in the .NET Framework 4.7, see Known issues in the .NET Framework 4.7.