Problems with backup drive.?

You need to be more clear on those vague pronouns there or what you are trying to say(I had trouble understanding so please make sure you edit in anything to clear things up for me). If your computer states that your external hard drive has only 8GB of room left when you try move 17GB of music into your external drive... well it makes sense. You need more room on your backup drive in order to put all your 17GB total worth of music on there.

Analogy I once used to explain to my brother : If your bag can only support 8 pounds of rocks and you are trying to fit 17 pounds of rocks in there... it won't work buddy.

You probably have another image backup on that external hard drive that is taking up so much space but isn't visible in Windows Explorer. Change your Windows Explorer's View options to show hidden files, folders and drives and also to show protected OS files so you can delete them.

based off of the info you gave it could be that the space required for your backup isnt large enough to handle that backup

it may be problem of file system type..

goto your external hdd properties check the filesystem type it may be ntfs,fat32,fat

if your using windows 7 formatt your hdd with ntfs filesystem and if it is xp then formatt it with fat32...