Here are some common errors, and how to fix them:
Error from park wrapper: You cannot park your main domain!
This means that you are trying to add your primary domain to your control panel. Stop trying to do that; your primary domain is already added to your control panel by default. If your primary domain is not working, it is because of a different reason.
Error from park wrapper: Using nameservers with the following IPs.... Sorry, the domain is already pointed to an IP address that does not appear to use DNS servers associated with this server.
Error from park wrapper: Unable to find out which user owns the parked domain
To solve this error message (usually received when attempting to remove a parked domain name), simply try adding the domain name to the Addon Domains section of cPanel. It will error out. After you receive the error message, go into the Parked Domains section of cPanel and remove the domain name.
Error from park wrapper: domainname.com is owned by another user
This means the domain name is already setup with hosting on your server, under a different user's account. Perhaps they own the domain and you do not. Otherwise, contact HostGator and we will look into the issue.
Error from park wrapper: Sorry, you are not allowed to add any more than (0) parked domains!
This indicates you are on a plan that only allows 1 domain name per cPanel. If you are on Hatchling plan, this is normal. If you are on a Baby or Business plan, this is incorrect and needs to be fixed by HostGator. If you are on a Reseller, VPS, or Dedicated plan, you control this feature and can easily raise the limit.