The IRS is stating that the person listed as the Primary taxpayer has already been claimed as a dependent on another tax return. In most cases this occurs when a child is claimed by their parents on the parents’ return, and then the child files their own return and does not check the box stating “claimed as a dependent on another tax return.” The parent has already claimed the exemption for this person, but the Taxpayer still needs to file to receive their own refund.
If the Primary taxpayer on this return has been correctly claimed as a dependent on another return you can fix this code: go to Basic Information > Personal Information screen and check the box directly stating “Check here if the Taxpayer can be claimed as a dependent on someone else’s return.” This box is located directly under the Occupation box entry. Then you will be able to resubmit the return.