Hi Glenn,
Take a look at the SAV logs on the clients. Are there any messages in there about the communciations layer failign to initialize, maybe with error code 0x20000022? If so the problem is likely cert related, like Pete said.
Communication technology is different in SAV than in SEP. There's no Sylink, for instance, in SAV. The following article may help:
Troubleshooting communication problems with Symantec Client Security 3.x or Symantec AntiVirus Corporate Edition 10.x
If trouble continues, check back on this forum or contact Technical Support. The issue might take some tinkering, but it's something that can usually be fixed in short order.
Thanks and best regards!
Mick