Problem With Posting

hey i have a relatively new wordpress installation with about 30 posts.. i can’t seem to be able to publish long posts..

for eg.. something like a huge list with about some 25elements. when i click publish it loads the 404 template of my current theme. (for this url /wp-admin/post.php)

the normal short posts work fine.. any idea what might be causing this problem.

i even reinstalled wordpress and started off with a fresh db.. but the problem persists..