Your social security number has been used as a dependent's on someone else's tax return.
Fix #1: Sign into your PriorTax account to see if your SSN and full name have been entered correctly. If you made a mistake, you can correct it on your rejection status page. Resubmit for filing.
Fix #2: If you are aware of who reported you as a dependent on their tax return, then you can contact them directly. They have the option to amend their tax return and refile it without claiming you are their dependent. Then you can resubmit your return for filing.