Is there some debug mode that will get ZA to indicate what error it encountered? I am having the same problem and if I could narrow it down, that would help. If I knew it was that ZA's calls to the ports was being blocked, I could diagnose that. If I knew it was a lack of access to the Internet, I could wade through the network traffic and debug that.
However, all it says is:
"Anti-virus/Anti-spyware update: Error"