[jpstewart]

You'll need to install the 64-bit version of libInventor, which should be on your IRIX installation media.  It's not part of Flame.  Unfortunately, I don't have an IRIX machine up and running at the moment and I'm a little short on time, so I can't provide detailed instructions.  Hopefully another poster can provide more info on where to find the right library and how to install it, without you having to re-install the whole operating system, now that we know what's missing.

If all else fails, try copying /usr/lib64/libInventor.so.3 from your friend's machine to yours.