Mine came with A102 but i have read about others using A101 with same problem. I ended up getting this:
http://www.eeshops.com/sony-nec-bdr-...00s-p-368.html
Dell lists them in their Driver Firmware page for the XPS1645 so i know it will fit. I will report back in a couple of weeks (still has not arrived) if this drive works but i googled and found nobody with any issues.