Hi,
Test SEP to GUP and GUP to SEPM communication
http://www.symantec.com/docs/TECH153328
You also should be able to telnet to Port 2967 on the GUP and see the connection in the GUP logs.
Additionally, basic network testing of the network segments between the SEPM, associated GUP and associated SEP clients should be accomplished.
for example: {While at the command prompt at the SEP client.} Tracert GUP_IP or GUP_FQDN
Trace Route (Tracert) will display the number of hops from the source to the destination. It will also show the amount of latency involved on a per hop basis.
Ideally, there will be as few hops between associated systems as possible and the latency will be under 20 Milliseconds per hop.
Make sure SEPM and GUP client is having the correct policy serial number.
Check this article as well:
Group Update Provider is not updating all the clients
http://www.symantec.com/docs/TECH140798