There's a problem with the windows wallet version 1.6.6.7.
EDIT: So I've downloaded 1.6.6.7b and the new bootstrap. Now it only makes it to block 820988 before the same problem occurs.
Which version do you use? 1.6.6.7 or the latest 1.6.6.9b?
https://github.com/philosopherstonecoin/philosopherstone/releasesI remember that I had problems with the bootstrap file some years ago, too. So I synced all blocks completely. It took round about 3 days.