to clarify:
1 server
29 clients
8 clients show up GREEN in the SBEP console
21 clients show up GREY
When you click on UPDATE in the maintenance panel on a client that IS NOT showing in the console, the server that is contacted and downloaded from is the SBEP server that you installed on your network?
Show us some log files: C:\ProgramData\AVAST Software\Avast\log (windows 7)
You can also generate a support package from the MAINTENANCE part of the interface MAINTENANCE > SUPPORT > GENERATE
make sure you uncheck minidumps
NOTE: the logfiles contain internal DNS names from clients and the avast server. If you dont feel comfortable sharing that replace the names with logical names and post it here
IF the clients update from your internal server, then something must be wrong with the ports that the clients use to communicate with the server.
Have there been previous Avast installations on those stations? or any other AV vendor?
if so, try cleaning/removing that with a special cleaning tool (avast uninstall utility, but other vendors have their own uninstall tool) and reinstall again