KACE Product Support

We are currently doing a trial of a Virtual K1000 running on an ESXi 4.1 server. The K1000 is v5.3.45496.

I have successfully provisioned only one client for testing. The one working client is running Windows 7 SP1 EE x64, and the installed agent is v5.3.44367 . I tried to manually provision two other Windows XP SP3 clients for testing, but neither of the WinXP clients report back to the K1000. I've tried many things on the XP boxes: disabling the firewall, uninstalling/reinstalling the agent, reading and following every trouble-shooting document I could find, etc. The K1000 resolves vis DNS to all three clients and from my understanding everything is fine as shown in the amp.log file. The only errors I see are in the kcopy.log file, as shown typically below:

[Fri Aug 26 15:30:56 2011] UploadFile: Uploaded to http://grsk1000.accorporation.com:80/service/inventory.php?KUID=2D2B355A-DB10-4BFD-895D-126BE38E5E61&VERSION=5.3.44367 Upload speed: 651811.000000 bytes/second
[Fri Aug 26 15:30:56 2011] Error (cURL) copying files from 'C:\Documents and Settings\All Users\Dell\KACE\\inventory.xml' to 'http://grsk1000.accorporation.com:80/service/inventory.php?KUID=2D2B355A-DB10-4BFD-895D-126BE38E5E61&VERSION=5.3.44367': (500) Unknown error

What is (500) Unknown error? What else do I need to look for?

Thanks.