Locking drive letters

Problem with USB storage device My Book Essential with WD Smartware. When the computer comes out of sleep mode, the drive letter, as an example, has changed from M to K or the reverse and at times the drive it self is not visable at all and can only be visable by rebooting the computer. This causes problems for my Backup software (Acronis). How can I permanately lock the drive letter. I have tried Disk Management to no avail. According to Western Digital the OS, Windows 7 32 bit, is overwriting the drive letter allocation and falls beyond their scope of knowledge.

Done that. Problem still exits.

One partition on primary HD and two USB devices. Z sounds like a good idea, I used it on the last external drive I had before it bought the farm.

Z did not hold. I am at a loss

I don't know if this will help you, but I installed an Epson wireless network printer a while back, and because it has card reading capabilities it shows up in the OS as another drive. That was causing some drive letter issues for me, so I changed the printer's letter to W, and now my external drives are assigned predictable letters once again.

It also might be of help if you could post a screen shot of your Disk Management" window.

I use a HP Officejet J6480 which is a wireless network printer and has card reading capabilities however no drive letter has been assigned to it.