Why Can't I Download Songs from ITunes to my External Hard Drive?

I have my music collection stored on an external hard drive. Recently, out of the blue, ITunes has declared that I do not have permission to download songs to that drive. This happens both when purchasing from ITunes and when importing CDs. Now I have to save them directly to my Mac, then move them to the external drive. This creates a heck of a lot of unnecessary work. I am able to copy, save, etc. from the Mac to the external drive, just not import songs directly onto the drive (even when I indicate the drive as the location of my music library). Any ideas?