SERIAL NoT ACCEPTED =

Install as a trial then enter the serial afterwords.

You will be prompted for the serial after a few launches
or you can start the app then wait 2 minutes then go to
HELP then ACTIVATE then enter the serial.

Or do this;

Go to the CS5 LICENCE RECOVERY folder then the DLL FILE folder and copy the
32bit dll file and replace each instance of that dll file in your adobe programe 
directory, then if you have 64bit copy the 64bit dll file and replace each instance
of that dll file in your 64 bit programe directory.