Endpoint Protection

I'm having a strange problem with a few of my clients where they will show up in my group and online, but If I check again about 30 min later the client is either not there anymore or it says that it is not online.  It mostly just disappears from the console. 
I'm not sure if it matters but I installed MR2 MP1 initially on them, but then upgraded to RU5 to try to solve the problem.  That didn't help, I also tried to uninstall the client completely and then reinstall.  Same result. 
These are windows server 2003 64bit servers that only have the antivirus and antispyware part installed and they are citrix server running Presentation server 4.5.  I have multiple groups and a total of about 150 clients but there are only 3 that I am having this problem with.  These 3 are all in the same group.  Every other client in the group is fine.  They initially did not have the same Policy serial number, so I reinstalled the client and now it has the same SN for the policy
I have tried to replace the sylink file, I am able to telnet to port 80 of the management server and I am able to view the secars webpage with no problem.  Any suggestions?

After the clients disappear, do they reappear?  If so, after how long do they reappear?

Is your SEPM installation using port 80, or port 8014 (the default since MR3, if memory serves)?

This document may be of help in trying to debug this:

Title: 'How to debug the Symantec Endpoint Protection 11.x client'
Document ID: 2007090611252048
> Web URL: http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007090611252048

sandra

Check the Sylink.xml file on the client, and look for the server it is contacting as well as the policy number.
Then check that policy number of the group you assigned to it is SEPM.
If they differ, then this may be the problem.