Please help me how to fix this problem

sir i share my problem about using norton ghost symantec version 11.0. I have a server running windows7 ultimate 64bit, the C:\drive- 500GIG, D:\drive- 500GIG(Archive), and Z:\drive-Storage 4T (Raid5), now i take image for backup using norton ghost Symantec is no problem. after 5 months the server there have a problem and i re-image these but there a big problem happen. the problem the D:\drive is become Z:drive, and Z:\drive is become D:\drive is twisted by itself, i re-image 3 times but the same result. now i need information the cause why is chnage by itself?and how to fix this problem?thank you very much