SCSI miniport & physical addresses

I have a SCSI miniport driver (running on NT 4.0) that uses
ScsiPortGetPhysicalAddress() to generate a scatter/gather list representing
the DataBuffer. Every once in a while, I get back a physical address that
is less than 1 MB. Whenever I send one of these addresses to the HBA, it
generates a DMA error. Is it normal for NT to use physical addresses in
this range? Is there any way to force NT to not use physical addresses less
than 1 MB in this situation? Or should this be valid and the hardware has a
problem?

Thanks for any insight.