Failed - sort of - installation of Endpoint Security on remote machines.

I have a location I’m managing for a client, with 4 computers, plus a CESM server. The CESM server is 2008 R2 server, 64 bit, 2GB RAM, running virtualized in VirtualBox on a Linux host.
The client computers are mixed:
2 are new Dells, with 8GB RAM, 1TB hard drives, and 8 core i7 processors, running 64 bit Windows 7.
The other 2 are Core2 Duo machines, 4GB RAM (3.5 usable) and XP 32 bit.
I have no problems with the Windows 7 machines. Installed agent, CES, and manage them with no issues.
The XP machines, however, refuse to properly install CES. If I install it remotely from the console, it goes through the entire process, no error messages, and finally says that the installation is completed. When I go back to the computer listing, though, it says “Not installed” in the Security Product column. If I check the client machine, it shows the agent running, which also shows as connected, but the CES icon shows as attempting to connect to the server. If I start up CES on the client machine, it asks to activate. I attempt to activate with an ESM server, and it says it needs to download and install the agent, (which is already installed and running, mind you) and afterwards, it still says not installed on the ESM console.

It’s like the agent and CES refuse to communicate with each other on these two XP machines.

I did manage to get the CES window up and running, and it says it’s updating (although I can’t remember exactly what it was that I did that finally resulted in this) but it still says “Not installed” in the CESM console.

When I first installed on these two XP machines, it had this issue, but it was inconsistent. Sometimes you’d turn the machine on, it would say it wasn’t installed, but after the next reboot it would say it was installed and up to date. Then after another reboot, it would be back to saying not installed again.
However, it’s been consistently showing as not installed for the past 3-4 weeks, regardless of what I’ve tried to fix it. I’ve made sure there isn’t any other A/V software, no other firewall (although the agent’s “About…” screen on the client machine says it’s connected to the correct server, so I doubt it would be a firewall blocking it, anyway), etc. I’ve tried uninstalling and reinstall CES on one of these machines several times, both as a remote install from the CESM console, and as a local install from the package downloaded from the CESM server console.
I’ve also tried completely removing the agent and reinstalling as well, with no change.

Incidentally, these two machines used to have AVG Internet Security on them, and although I’ve completely removed it, including running the AVG removal tool to “rip it out by the roots,” so to speak, the Windows Security Center console still says “AVG Firewall is turned off” when Comodo isn’t installed. Not sure whether that’s relevant to my problem or not. (This is at least true on one of them, but I can’t check the other right now, as I’m working remotely, with nobody at the physical location of the computers, and the other XP machine is turned off.)

Forgot to include:

CESM is version 3.2.1117.157.

CESM console says it’s up to date, and the client machines are also up to date as far as patches go.

Any ideas? Anybody?

Still haven’t solved this problem. I know CES works on XP, as I’ve got an XP machine here at home that I’m using it on, with an almost identical setup, only less RAM (1.5GB) and a slower processor (Celeron 2.4) on my XP machine that these two I’m having trouble with at the client location.

I did find, using Sysinternals Autoruns, a couple of AVG files that weren’t removed using the AVG removal tool. However, deleting references to these, and then the files themselves, has made no change at all.