When I create a bill of materials for my assembly, I get 3 blank rows that show no part number, description, etc...
I've gone over my drawing and everything else it accounted for.
I do have a few sub assemblies within my main assembly, could that be causing the problem?
It depends on where your template for the bill of material is pulling its information from.
It sounds to me like you have all fields pulled from custom properties and you have 3 components (could be sub assemblies or parts) that don't have those custom properties assigned.
alternate question: Do you ALWAYS get 3 blank rows using that BOM template? If so, then the problem may be in the template itself instead.