I did some researsh and found a solution posted by Léonie early october, and it worked.
This solved my question by leonieDF on Oct 7, 2012 12:25 AM
You may have a corrupted "ProAppSystemID" file or Aperture cannot write to the System Library.
To stop Aperture asking for the serial number, first check, if you still have an old file "ProAppSystemID" in your System Library.
- Quit Aperture.
- Go to your MacintoshHD and open the folder "Library", then "Application Support", then "ProApps".
- Remove the File "ProAppsSystemID" to the Desktop, if it exist and restart Aperture.
- Reenter your serial number, hopefully for the last time.
Sometimes Aperture writes this file to a temporary directory, when it cannot write to the Library. If the above does not work, look at the temporary directory /tmp
Use the Finder's "Go" menu
Go > Got to folder and enter /tmp into the textfield. If you see the file there, move it to its proper location.
In this case you may want to repair the permissions on your system drive; you can do this using the "First Aid" tools in "Disk Utility" (located in Applications > Utilities)
when you enter the registration code, are you signed in from an administrator account? Aperture is installed for all users, and so the ProAppSystemID needs to be written to the system library, not to the user library.
The problem: When you are logged in from a regular user account, Aperture is not able to write to this folder. You either need to change the permissions on the "ProApps" folder, so that you have read/write access, or be sure to enter the registration key logged in from an Administrator account.
Repairing the permissions with DiskUtility will not help; it will set the permissions in a way, that only admins can write to the system library.
Do your serial numbers include any easily confused characters? Like O and 0, or l and I?
See this list:
The matter got worse; now it doesn't recognize my codes and I can't open it at all...
What have you done other than trying to enter the serial number?