<p>Here's the scenario. I'm using myopenid for, among other things, StackOverflow. When I initially set up my openid account with myopenid, I decided to try out Cardspace because they had support.</p>

<p>I later wanted to access Stackoverflow from another machine so I chose to back up my card. I gave it a password and a filename and successfully created a backup file. I was also to able successfully import it to my laptop.</p>

<p>Here is where the problem comes in - I am unable to use the card that I backed up from my laptop. The original card still works great on my desktop. Additional information is that my desktop is running Windows XP SP3 (x86) while my laptop is running Windows Vista (x64).</p>

<p>Any ideas? Am I doing something wrong? I'm seriously considering dropping Cardspace on myopenid and moving to a password solution with them instead.</p>

<p>Thanks!</p>

It
should
work; however if you have 3.5SP1 on one machine and 3.5 or less on another there was an (unannounced) breaking change with the code to generate the unique ID from the card; which may explain why it doesn't work.
I would try sending a test transaction to
the SharpSTS test page
with only the PPID as the claim, and examine the token sent back; if the PPIDs differ then that's your problem.