I'm assuming ace is your environment name? It's not a Cadence tool name.

What you need to do is:

a) Install an Assura version intended for use with IC446
    rather than IC50. There are separate builds - you can
    see this on the http://downloads.cadence.com site
b) Make sure that the ASSURAHOME environment variable is
    set and is pointing to the root of the Assura installation
    tree.
c) Make sure that $ASSURAHOME has the tools link pointing
   to tools.sun4v (or whatever platform you're using).
d) Make sure your UNIX path contains:
    $ASSURAHOME/tools/assura/bin

That should be sufficient.

Of course, I don't know whether "ace446" is altering the path or environment variables itself - you'll have to check that.

Regards,

Andrew.