duplicate global::system.runtime code example

Example 1: while coding c# i get the error : "Duplicate 'global::System.Runtime.Versioning.TargetFrameworkAttribute' attribute [first_better_project]"

<GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>

Example 2: while coding c# i get the error : "Duplicate 'global::System.Runtime.Versioning.TargetFrameworkAttribute' attribute [first_better_project]"

<ItemGroup>
  <DefaultItemExcludes>$(DefaultItemExcludes);obj/**</DefaultItemExcludes>
</ItemGroup>