Are you getting a warning or an error? If you're getting a warning, you can disregard (or skip) the warning if it doesn't apply to you.
If you're getting an error that you can't skip, you may have inadvertently answered yes to the question Did you dispose of a property in 2017, that was your principal residence for any of the period that you owned it?
To confirm you've answered no, use the menu across the top of your screen when you're signed into your return and select Setting Up > Other Questions.