Symantec Endpoint Protection 11.01 Corporate; Windows XP SP2; Windows Small Business Server 2003; Log on Issues

Hello and thank you for reading my question.

Yesterday morning, my client updated SEC. Since then, we have had the following symptoms:

1) Computer hangs on "Preparing Network Connections"
2) When the user is able to authenticate, the computer hangs for a long time, often resulting in a blue screen without text
3) When shutting down, the computer hangs on saving settings

Some particulars:

1) SEP was completely uninstalled prior to installing the new version
2) running the Symantec Cleanwipe utility with a reinstall does not change anything
3) a complete uninstall of SEP removes all symptoms
4) if one unplugs the network cable from the client computer prior to booting, it is possible to boot without network resources; reattaching the cable allows LAN access
5) all machines had the un-managed client installed, i.e., we are not using the SEC server option in this install
6) one of these machines had the same upgrade four months ago, and it works just fine; none of the above symptoms
7) all client machines are running windows xp SP II
8) the version of Symantec Endpoint Protection is 11.01
9) I can't recall the build of Windows Server 2003
10) SEC is not installed on the server

A few hunches:

1) I suspect that this has something to do with SEC as uninstalling it allows normal functionality
2) this probably has to do with how SEC functions on the network--disconnecting the network cable allows for regular log on

I would greatly appreciate any advice that you have in this regard.

Best,

Fritz the Blank