Can't Figure anything out

My brain is fried - I can't figure out why a problem is occurring. This has become the bane of my existence with iSCSI and the windows device model. Sometimes things just work and other times, they fail - for no logical reason. I'm trying to get the Device Instance Name from a Device Number (in this case a Disk) but the results I get are flaky - sometimes I get the name and at others, I don't. And what I get depends totally on whether I compile with UNICODE or without, but there is no conclusive and deterministic answer to my problem. I hate it when I am reduced to a babbling fool, adding and deleting tiny breakpoints to pinpoint the actual problem - why can't it be intuitive?