Re: Scan stuck at smss.exe
please try to boot in SAFE MODE with NETWORKING, open ZA manually (firewall will not be functional but the antivirus scanning yes) and then start the scan. See now if it still hangs on that file. I would recommend to wait some minutes before concluding that ZA is hanging. The scanning of some file can take a long time.
Hanging may be related to corruption of file, hard disk issues, malware infections or simply the file is busy and cannot be scanned. The latter can be solved by running the scan but in SAFE MODE with networking as suggested above.