How to fix "Could not load file or assembly System.Core" error?

Question

System.Core shows as missing in References. I removed and tried to add it again but I can't see System.Core in the list of default assemblies. It complains about this for Linq.

This project compiled OK with the prior VS version, but fails with VS 2013. Is this moved or how else would I miss this DLL?

Answer 1

System.Core was added with .NET 3.5.

Answer 2

3.0 is not enough, System.Core (LINQ) was added in 3.5. Please upgrade target framework in project properties.