Did you share the policy with a family member who filed their own return? Did you receive more than one 1095-A?
Or, you may have already entered your 1095-A and are making a Duplicate Entry.
Type '1095a' in the Search window, then click on 'Jump to 1095a' to view a Summary.
If not, try Deleting your 1095-A entry and re-enter it.
To delete a form in TurboTax Online, click on Tax Tools > Tools > Delete a Form.
For TurboTax desktop, switch to FORMS mode, open the form and choose Delete at the bottom.
You could also try contacting healthcare.gov or your state's Marketplace.