On your tax return, the primary SSN has been used as a spouse's SSN on another tax return in which Married Filing Separately is the filing status. If one of the spouses already filed using Married Filing Separately as the filing status, then the other spouse cannot file a separate return using a filing status of Single, Married Filing Jointly, or Qualifying Widower.
Fix #1: Sign into your PriorTax account and update your filing status by following the on-screen instructions. You will then be able to resubmit your tax return for filing.
Fix #2: Your spouse could amend their tax return to update their filing status or so that you can both file a joint tax return. To do so, your spouse should contact the taxpreparer they used or the PriorTax customer support team to get started.