Again, why didn't you follow john's and my suggestions? If you did, what happened?
Ignoring InCD momentarily, which Nero version are you running? Does it allow you to upgrade to the latest 18.104.22.168?
You might have been confused by the statement on Ahead's site:
"Updates run only on systems where a previous version of InCD is installed."
As indicated by john and me, this is not really correct. Once a suitable version of Nero is installed, InCD should not refuse to install.
Another possible source of confusion is that Ahead offers InCD updates only, but Ahead's meaning of "updates" is strange (there are no stand-alone versions).
So I repeat our suggestions. First, remove the old InCD via Add/Remove Programs in Control Panel. Then peek at Program Files\Ahead and its subdirectories, and delete any traces of InCD (I don't know where InCD 2.24 installs by default). Now, make sure that Nero 22.214.171.124 is installed and working properly. Then run InCD3.51.61UP.exe, choosing the default installation directory (Program Files\Ahead\InCD). If you still get an error, report the exact message to us.