Listen to what is being said! It is the file system in your A500 that is causing the problem! HDToolox is NOT the problem. There is a 64 bit patched FFS, that will work if you just replace the FFS on your boot drive with this file.
I am not 100% sure of the file name (Maybe 64TDFFS ? or something close). Your other option is to use a third party file system that supports drives >4Gb.
This will cure your problem.
OR - go to OS 3.0
