I am getting "defined in an assembly that is not referenced" errors when building my c# project, how to solve it?

Question

I have already have references to System and System.Data.

1.The type 'System.ComponentModel.IListSource' is defined in an assembly that is not referenced. You must add a reference to assembly 'System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

2.The type 'System.Data.Common.DbDataReader' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

3.The type 'System.Data.IDataRecord' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

4.The type 'System.Data.Common.DbConnection' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

I have already have references to System and System.Data.

Answer 1

Restarting Visual Studio resolved the issue for me.