First of all, I've found these two websites for the problem:
According to these links, the problem is based on a change by Partition Magic: it has changed the Windows XP boot partition, and windows has been shocked largely, because it has left the partition in an unfinished state. However, I don't know yet whether windows is surprised because the partition has been changed or because errors occured that have not been corrected appropiately.
I've taken a look into this page, and there is an explanation how to correct exactly this problem: