Attribute rules not working

[michaelcsikos]

I have two solutions which are set up virtually identically. The EXE and WinForms DLLs are .NET 4.8, the other layers are .NET Standard 2.0. It's (still) using CSLA 4.11.2. In one solution attribute rules, e.g. [Required], are not working. I have copied the same class to both solutions. It works in one and not the other. The app.config and bindingRedirects are identical. Any ideas?

[rockfordlhotka]

Have you confirmed that the dependencies (like System.ComponentModel.Annotations) are identical - same versions, same NuGet package names?

[michaelcsikos]

Thanks for your quick reply. In the output folder System.ComponentModel.Annotations are indeed different. The projects weren't explicitly bringing them in, but the project where the rules work is using Microsoft.EntityFrameworkCore which depends on version 4.7.0. Adding 4.7.0 to the Business layer in the faulty solution via NuGet solves it.