Do you mean you get an error message that says Numbers can't run because some files are missing? This is a common error when a user has moved one of the iWork applications from one disk or computer to another. The solution is to install from the original media - disk or Mac App Store.
You may need to delete the copied application & then reinstall from the boxed DVD or the Mac App Store. The easist way is to use Yvan Koenig's AppleScript that removes the files. You can find it on his box.com account in for_iWork'09 > other_iWork'09 items > uninstall iWork '09.zip.