Transfer of Library to a back-up External HD

My iTunes library (about 500 gigs) is loaded on a Raid-1 Cavalry external HD. In an attempt to get additional back-up I purchased a new FreeAgent Desk 1 TB external HD. The Mac recognizes both HDs, however when I attempt to click and drag from the Cavalry to the FreeAgent the response on the monitor is, in so many words, the transfer can not be completed because the FreeAgent cannot be modified. This was supposed to be super simple according to the Geek at Best Buy. Am I doing something wrong here? The Cavalry is connected to the Mac via Firewire, the FreeAgent is connected via USB.
Did you format the new disc first using Applications=>Utilities=> Disk Utility
What Shadorne said. If you do that it may repair permissions on the FreeAgent. That's what your problem sounds like off the top. Permissions allow the various users of the computer to read only, write only, read & write, etc.
Sounds like iTunes only recognizes one library.
Try the eport utility in iTunes:
'File\Library\Export Library'
good luck
I think DRM is at work in not letting you do the copy. Check the iTunes blogs for details.
My guess would be that the FreeAgent HD is preformatted to Windows-compatible. With my MacBook, I have a Windows partition that doesn't allow me to copy files directly between the Mac and Windows partitions.

Like the previous posters, use Disk Utility to reformat to Mac-compatible and the disk permission issue should be fixed.
Thanks to each of you. This is a thread that I wish I could have pulled before it got "on the air". The box clearly stated that the FreeAgent was formatted for Windows and Vista - Duh! Two geeks at Best Buy AND me did not think to check that. I returned it and got a "My Book" formatted for Mac OSX. Wallah! It copied and pasted from the Cavalry without a hitch. The "My Book" is back in the box and tucked away as that extra back-up that we should all have. With the Raid-1 Calvary and the el-cheapo "My Book" I think the library is safe. Thanks Again - Don't I feel like an Audiofool.
That's good news! I am backup crazy too. The My Book II is also RAID 1 and recently I replaced one of the drives with a new one. The extra darn near up to date drive is sitting in a secure location.
Personally I use SuperDuper! it's great for backup of my 2TB of music. The best $28 I've spent on my stereo.