Hi netadict and welcome to Seven Forums.
I assume that you are using the Linux rescue CD. That can be problematic. One thing that you can try is completely powering off, attack the backup drive while powered off and then boot the CD. That worked for me sometimes.
The other thing you can do is to use the WinPR recovery disk which is much better at detecting your disks. Normally this would require rather a large download but whs has created a prebuilt ISO which you can find here. FileSwap.com : Macrium 5.0 WinPE.zip download free
. All you need to do is to burn it to disk.