Mailbox Role Setup Error

Hello, when trying to install the Mailbox Role: Transport Service, I get the following error:

Error:
The following error was generated when "$error.Clear();
configure-WSManIISHosting -EnableKerberosModule;
" was run: "Application 'PowerShell' doesn't exist in the default Web site in 'C:\Windows\system32\inetsrv\config\ApplicationHost.Config'. Make sure the application isn't deleted from the default Web site.".

Any ideas how to resolve this? I've tried everything.

Thank you.