Official comment
More than likely, the issue is that you do not have a "Basement Floor" construction feature. For example, if you change the basement floor to "Slab on Grade" and then try to add a basement that is below ground you will receive the error you are referencing because slab on grade is only intended for floors than are less than 2-ft below ground while a basement is defined as a room more than 2ft below ground on average. If you create a ticket and reference your project we can take a look.
Best Regards
Bill