ActiveX Control won't install

Hi

I'm trying to use the Remote Desktop ActiveX Control, embedded into a
website. I have about 40 users using it without problem, but one machine
just won't install the control on first visit to the page. I get the
following box popping up in the middle:

'Remote Desktop Web Connection ActiveX control could not be installed. A
connection cannot be made without a working installs version of the control.
Please contact the server administrator.'

See http://putfile.com/pic.php?pic=10/29805183444.jpg&s=x2

The workstation is Windows XP Pro SP2. All my security options for ActiveX
controls in IE are set to 'Enable'

Can anyone shed any light on why this is happening, or an alternative way to
install the control? I tried to copy msrdp.ocx and msrdp.inf to
c:\windows\system32 and do a 'regsvr32' which said it'd installed the
service, but I still get the box popping up when visiting the page.

Any help appreciated

Dan