Emax

I recently installed the zip upgrade, am I correct, on an emax hd 
model, you only need to replace the cable leading to the harddrive to 
a nexternal zip drive using a connector (only one cable actually has 
to be altered, right?) and install the emax plus os, however the emax 
software I b ought from emulator archive gives me the "wrong 
software" error. I doubt it could be their fault, but I've triple 
checked my work now and have done nothing wrong...
any help would be fabulous
~AJB