There is an issue that can occur with KML and BNA files. If a customer is using a faulty BNA file during studies they could be presented with this error message:
This error message is basically saying that the BNA file in use for this study was not properly closed. Now this error originally occurs in the KML file. And during the KML to BNA conversion, which can be found under utilities>KML to BNA, it works successfully meaning it doesn't throw errors. But it doesn't not catch the issue that we see in the BNA file.
The reason this error occurs is because either the polygon was never closed to begin with, or it may have sections where the polygon overlaps with itself. This essentially closes the polygon but not properly and that's why we get the error. This image shows the problem area for the original file, the polygon clips itself just below where the red cursor is:
In order to correct this problem you may find it useful to try converting the original file in QGIS to the same format, KML to KML. And then trying the utility KML to BNA conversion again. Or you could also request a new KML file from the vendor and be sure to inspect the whole polygon for any issues before beginning your KML to BNA conversion