an issue about difference SCSI IO between Windows 2000 and XP

Hello:
I am developping a SCSI port driver for a reading card device, when
inserting a SD card,on Windows XP platform,it works well, but On windows 2k,
it will receive SCSIOP_WRITE command,I think it is not normal. After
inserting a write-protected SD into reader device, on Windows XP platform,
it works well, but On Windows 2K, system can not access the card, it will
show a I/0 error message.
I wanna know that what are the differences between XP and 2K when
handling SCSI commands, or is my driver issue?

Thanks
BR

Leon