Gmail Error: You cannot create a mail account for

Hi, I am trying to use my cpanel email with gmail but I am receiving the error message "You cannot create a mail account for your email" whenever I go to settings>accounts>add a mail account Some Context Before my email was created in cpanel, the website already existed and I created my email in gmail. It wasn't until last week when I hired a website developer, that the problems began. To solve the issue, he created the same email in cpanel. Now I cannot receive emails when I am logged in to gmail. I can send emails from gmail, but not receive. How do I fix this? Thanks in advance! -George