During Installation After Effects CS6, after input Serial Number - report "we are unable to validate serial number for Adobe After Effects CS6. Please contact the support."

Those are the Adobe blocker entries which is affecting serial number validation process.

Follow below steps :

• Remove all entries which has adobe name . Then close the Textedit , it will Autosave.
• Make sure there are no Adobe entries inside .
• Then copy and paste the Hosts file back to Etc folder . 
• We are replacing edited hosts file which we had copied to Desktop with the original Hosts file inside Etc folder.
• When prompted , Authenticate with Mac password ,
• Make sure to select Replace option ..
• Once you has replaced Hosts file , double click on it again and check whether Hosts file is free from Adobe entries.

Then try to activate CS 6 apps using serial number, it shud work.

Let me know if you face any issue .