Recently I was reinstalling the WSUS server role on Windows Server 2012 R2 , I was able to remove the role and then install the role through server manager without any problems.
However, when I came to launch the ‘post installation tasks’ from server manager, the task was repeatedly failing and I was not able to open the WSUS configuration wizard.
To fix this, I removed the role once again, opened IIS and deleted the site ‘WSUS administration’ which still remained when the role was not installed. After reinstalling the role, the post installation tasks completed successfully.
Hope this helps!