Unity 2020.1 Collision2D and namespace UnityEngine error

[behdadsoft]

Hi.

I Made a 2D project with unity 2019 and now after update to 2020.1, unity gave me error below that seems can’t find Collision2D in namespace UnityEngine. also I updated Visual Studio 2019 and Physics 2D is enabled in Package Manager.
dose anyone know where is the problem?

The type name ‘Collision2D’ could not be found in the namespace ‘UnityEngine’. This type has been forwarded to assembly ‘UnityEngine.Physics2DModule, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null’ Consider adding a reference to that assembly

[behdadsoft]

For fix this issue, I created a new project and copied Assets folder from old project to new project. now all things are OK.