c# – Unity error: type “x” exist in both ‘A’ and ‘B’

I just opened a project made in unity version 2018.1.1f into unity version 2020.1.1f
I know opening the older prjects is not supported by unity but it opened fine.

The only problem is that it is giving an error which looks like this-enter image description here

What i tried:
1-checking the script onetizationPlatform.cs to ensure nothing is wrong in it
2-checked that there’s no two files with same name unitylifecyclemanager
3-doing point 2 with unityengine.advertisement.editor
4-deleting unityengine.advertisement.editor whuch caused another error so i had to restore it back