IPREFS fail 20 could be because you have kickstart 2 configured in winuae.
The boot disk needs winuae to start with kickstart 3.1.
WHDLoad fail 10 could be a few things, perhaps it didn't find a needed kickstart file on the boot disk, or you didn't start winuaex with enough fastram to preload the game. Didn't WHDload also pop up a box with an error message? "can't allocate expmem" and "object not found" usually mean it wants more fastram. If I knew what game pack it was I could try it myself.
The boot disk is an adf because winuaex has a bug where if there's no adf in df0 it takes longer to boot from hdf. Also it seems to always boot from the first configured hard drive no matter what boot priority you set, so you'd have to either boot from the game hdf, or fiddle with the configuration to swap the game hdf to drive 2 and configure your boot hdf in drive 1.
I just decided it was easiest to get round it all by making the boot disk an adf and setting floppy speed to turbo.