[support] Drupal 5.7 - cannot update nodes

[Domas]

Hi,
I've run into a strange problem on a small personal blog. When I edit a
node (any node) and submit it, I get redirected to the frontpage and the
node I was editing is not updated. No errors in drupal's log or in the
server logs (though they do not log mysql errors). 

The strange thing is that I can create new nodes but then I still can't
edit them (the changes are not saved). Revisions are enabled, but I've
tried disabling them with no luck.

Any suggestions? Maybe somebody knows what could be wrong? The site
worked fine for some time. No major changes were made before this
happened (just editing menu items, nodes).

Thanks in advance,
Domas