SharePoint 2013 – Error while creating a new site collection “User cannot be found”.

Issue: Error while creating a new site collection “User cannot be found”

Description: I was able to create a new site collection on another farm using the same account. Also I was able to create a new site collection on a new test web application on the problem server with this user account

Solution: Turns out the issue was due to enabling Trusted Identity Provider (STS) for Forms login for external users  on site. For some reason, after enabling STS,  SharePoint was failing to identify Windows NT id.

Once I Turn off the STS,I can able to create the Site collections.

 Click on Top of WebAPP->Click on Authentication Providers->Click Default->Uncheck Trusted identity provider

 

I hope the above information will help you to resolve the issue, in case of any queries/questions regarding the above mentioned information then please let me know. I would be more than happy to help you as well as resolves your issues, Thank you.