The customer has managed a client that appears to be disconnected from the Notification Server with no reason as to why. 

"11/14/2014 11:26:21 AM ConfigServer AeXNSAgent.exe Configure Server Mode: Failed to obtain machine resource GUID AeXNSAgent.exe"

"11/14/2014 12:42:47 PM ConfigServer AeXNSAgent.exe Configure Server Mode: No policy key is found or policy key was changed, will reinitialize machine GUID AeXNSAgent.exe"

"11/17/2014 10:04:20 AM ConfigServer AeXNSAgent.exe Failed to find the server key: url HTTP://<smpserver>.<yourdomain>.com/Altiris/NS/Agent/CreateResource.aspx AeXNSAgent.exe"

"11/17/2014 10:06:20 AM Agent AeXNSAgent.exe Failed to register agent. Registration status 'Pending'. Next retry in 4 min. AeXNSAgent.exe"

"11/14/2014 12:14:06 PM","Policy reading suspended:

Altiris.NS.Exceptions.NSComException (Altiris.Common): The specified resource is not ready: guid=204e1e5f-2803-452a-9b19-d263b418e9f4, type=493435f7-3b17-4c4c-b07f-c23e7ab7781f. This condition is temporary and will be resolved by the next collection update."

SMP 7.5 SP1 HotFix3

The Agent Registration policy on the NS was disabled.

Enable the Agent Registration policy (under Settings>Agents/Plug-ins>Symantec Management Agent>Settings>Registration Policies) and run a Full Membership Update.

Upon checking a few more client machines we see they are disconnected, but upon them requesting an updated configuration we see communication takes place and they are once again connected.