If you’re unable to create an email account inside of cPanel (followed by an error highlighted in red) it is likely you’ve modified the file structure of the cPanel account.
Folders just above the public_html directory should NEVER be modified unless you specifically know what you’re doing.
If you get an error when creating your email account, you may need to delete the cPanel account and re-create it. Please note that any data inside the account will be lost if you terminate. Sometimes our support team can manually re-create folders allowing email accounts to be re-created.
Ultimately it depends on how much damage has been done to the overall folder structure of the cPanel account.