My Symantec Tech just got in touch with me and said they are still working on this issue. I have since upgraded to 12.1 RU1 and still have the issues, so this is getting pushed to the development team.
Other things I have tried:
- With the clients receiving the errors, I have updated the network card drivers and also manually set the duplex setting to match the connection of the SEPM.
- Moved clients (with the errors) to a new distribution group.
- Uninstalled with CleanWipe and reinstalled from DVD and then manually added the communication setting.
- Uninstalled with CleanWipe and pushed installation from SEPM.
One thing that is interesting to me is that I still have some clients (mainly servers) on version 11.0.6300.803, which I haven't had one problem with. All the clients I have errors with are version 12.1