Decrypt files/folders

I have a client that encrypted there my documents folder on their pc. Then it
was upgraded to Windows Vista Business from XP Pro. Now they can't access
their files. I tried to take ownership of them and decrypt them No luck. I
first tried to just decrypt them but it said I need administrator access.
They are a administrator on their pc. Then I tried to do the owner ship and
then decrypt. Still says they need " You will need to provide administrator
permission to change theses attributes. Click Continue to complete this
operation."

I am stuck at this point, I have gone in circles with this. They are
desperate. Any help would be greatfully appreciated.

I hope I can find a backup of their old PC before they upgraded.