Why won't apps open?

Hey guys
I was giving my mac to a guy and was leaving the apps on there for him. I created a new account and all the programs opened fine. Then I deleted my user account and now he can't open any of the programs. So I got out the external hard drive that I used to back up before giving it to him and booted the computer using that external. Now when I try to open Final Cut, it won't open for me... ideas?

If you are turning over your apps along with your Mac, then you cannot keep a copy for yourself and must turn over your installation discs or license keys, etc. to the new owner because they are tied to those apps. We comply with US law and it is illegal to share purchased software/apps. Only one person may own and use them at a time.

EDIT: My point is/was as long as you are providing the new owner with all necessary software, etc. he/she should have no problems installing or re-installing FC or any other app on the Mac.