So Cleaning out your TEMDIR no longer resolved the issue for you?
If Uninstall and cleaning the computer with my 6 step intructions posted in my May 29th 8pm message, then you may be correct in assuming a Hardware problem?
However it may also be possible that either some other Software or MALWARE is conflicting with ZA AV Updating..
follow all the steps as detailed here:
Malware Clean-up Guidance <= click here
(including posting your logs at bleeping computer or spywarehammer to get your system analysed by experts)
Let us know how you have managed to resolve the issue. It will help other users with the same problem.