Several issues here.
1) You are not using the correct method. That article is, "iTunes for Mac: Moving your iTunes Media folder". Your media folder is only part of your library. You need:
iTunes: How to move [or copy] your music [library] to a new computer [or another drive] - http://support.apple.com/kb/HT4527
Quick answer if you use iTunes' default preferences settings: Copy the entire iTunes folder (and in doing so all its subfolders and files) intact to the other drive. Open iTunes and immediately hold down the Option (alt) key (shift on Windows), then guide it to the new location of the library.
Windows users see tip at: https://discussions.apple.com/message/18879381
2) I suspect you are trying to copy to a NTFS formatted hard drive. If this was used for the PC then it is NTFS formatted. Macs cannot write to NTFS, but can read it. You will have to wipe the external hard drive and re-format it to a format both can read. FAT32 might work for an iTunes library.