The Cisco IOS Software Releases 12.4 Mainline has been retired and is no longer supported.
End-of-Support Date: 2016-01-31
Cisco's End-of-Life Policy
You can view a listing of available Networking Software (IOS & NX-OS) offerings that best meet your specific needs
If you want support information for the Cisco IOS Software Releases 12.4 Mainline documentation, it may be available through Cisco.com Search or in the Cisco Community