Vista - EasyTransfer does not work on source partition

I have tried to start the EasyTransfer function on my old XP partition (C
as the source and chose the option to use an external medium (harddisk) to
store my 'old' data. However, once I select to transfer all accounts, files
and data I get an error 'error during checking the system...' (translated
because I'm using German Vista) and EasyTransfer stops.

Any idea how to make this work ?

Thx,
Andreas