Rami, Did you solve your problem yet ?
Here I have the exact same problem:
the downloadable latest ESET NOD32 AntiVirus is 4.0.93.x;
this Linux version does NOT accept License Key (Activation Key), and only accept Username & Password;
seems ESET already replaced Username + Password with License Key, as a general policy;
seems no tools for converting License Key back to Username + Password;
seems no newer version of AntiVirus, which accepts License Key, is available for Linux;
seems ESET Customer Service is not responding.
Overall it's quite confusing and I already spent 1/2 day in trying to activate this thing. Now still waiting for ESET CS to reply .....