problems movimg itunes media folder

Consolidate ("organize") is how you move your iTunes media files (not the whole library) to a new location. Consolidate simply looks at everything you have in iTunes and copies them to the iTunes media folder location specified in iTunes prefs -> Advanced.

iTunes 11 for Mac: Change where your iTunes files are stored - http://support.apple.com/kb/PH12165 - more information at: https://discussions.apple.com/thread/5036221?answerId=22026652022#22026652022 - and steps 5-8 in https://discussions.apple.com/thread/5782936?answerId=24491967022#24491967022snowle

iTunes for Mac: Moving your iTunes Media folder - http://support.apple.com/kb/ht1449

You have sufficient space on the external drive?

By the way, another option is to move the whole iTunes folder (your whole library) to the external drive. This makes it easier to move your collection in the future, or use it with another computer, since it is all self-contained. It does, however, mean the external has to be on to use iTunes. If all your media are on the external then that prettty much goes for using iTunes in any configuration so you may as well use it self-contained. To do it this way, copy the entire iTunes folder and all its contents to the external drive, start iTunes holding down the option/alt key, then select the library.itl file in the copied iTunes folder.

What are the iTunes library files? - http://support.apple.com/kb/HT1660

More on iTunes library files and what they do - http://en.wikipedia.org/wiki/ITunes#Media_management

What are all those iTunes files? - http://www.macworld.com/article/139974/2009/04/itunes_files.html

Where are my iTunes files located? - http://support.apple.com/kb/ht1391

If you're still going with only copying media, I copied the below from the last link I provided earlier. You have followed step 5 and chosen the external drive?

1. Open iTunes.
2. Choose iTunes > Preferences.
3. Click the Advanced button.
4. Click the Change button in the "iTunes Media folder location" pane. The Change iTunes Media Folder Location window appears.
5. Choose where you want to save your new iTunes Media folder.
   Note: Your iTunes Media folder is named "iTunes Media" in ~/Music/iTunes/ (the tilde ~ represents your home directory).
6. Click the New Folder button in the Change iTunes Media Folder Location window. The New Folder window appears.
7. Enter the name of the new iTunes Media folder.
8. Click Create.
9. Click Open in the Change iTunes Media Folder Location window.
10. Click OK in the Advanced window.
11. iTunes 9 or later: Choose File > Library > Organize Library.
    iTunes 7 or iTunes 8 for Mac: Choose File > Library > Consolidate Library.
12. In the Organize Library (or Consolidate Library) window, select "Consolidate files."
13. Click OK.
    Important: All of your media files should copy to the new location. There must be enough hard disk space available to copy all of your media files.
14. After the folder copies, find your original iTunes Media folder and drag it to the Trash.
    Important: Keep the iTunes library files that may be in the same location as the iTunes Media folder. Learn about the iTunes library files.
15. Quit iTunes and open iTunes again.