Thanks very much for the suggestion; we tried that. We had to open a TAC case and got this solution from Cisco, which worked:
This problem might be due to an improperly registered msxml3.dll .
Please try the following procedure to reregister msxml3.dll and then rerun the agent install
1. Uninstall the Cisco Nac Agent from the system.
2. Just to be sure manually wipe out directory "C:\Program
Files\Cisco\Cisco NAC Agent" in case the uninstall left anything behind.
3. Download regrserv32a.exe from
http://support.microsoft.com/kb/267279
4. Run regserva.exe - this will extract regserv32.exe on disk
5. Open a command prompt and cd to the directory where regserv32.exe
extracted.
6. Run regsvr32.exe msxml3.dll (it will pop up a dialog saying the
registration was successful.
7. Then re-install the NACAgent.
8. Agent should now pop up (script error symptom should now be
eliminated)
Regards,
Manivannan Srinivasan
Cisco TAC