True Image Home 2011 - Backup of Files not working (Drives A and B)

Hi. I'm using Acronis True Image Home 2011 to perform backup of my files/partitions. When I try to make a Partition Backup of my drives A or B (which are 2 different HDDs), the program works normally.

But, when I try to make backup of only some files (File Backup) the program won't recognize these drives... I've already tried to find any settings to make it recognize'em but in vain.

So, how should I proceed to make ATIH 2011 recognize my A and B partitions to make this File Backup?

Thanks.