Hi,
Sometime we are getting this error while adding a new domain or creating a site for the domain. This means, the domain you are trying to create it already exist in the server. To fix this error you need to remove the domain from IIS.
Please follow these steps to remove domain from the IIS:
1) Login in to the Server via RDP with Administrator user.
2) Open the IIS Manager.
3) Click on the domain name > Remove.
Now, try to add this domain again. I am pretty sure you will not get any error while doing so.
Thank you,
