To be able to change the systems runtime configuration (what MarketEnabler does) you will need access as a root user to the system.

MarketEnabler expects that you will have a file called "su" on your system (and in the global path) that will open a root shell.

The commands that are used, are not always part of the Android system.

Most rooted phones have busybox on board as it's common to install it during the rooting process or included in most custom roms.

If you don't have busybox, I recommend using the busybox installer from stericson on the market.