Problem in posting after upgrade to 3.0

Hello, i am facing problem in posting new post after upgrading my wordpress to 3.0. Whenever i write a new post and try to save it as draft or publish it it gives me 404 error how ever title of the post is saved in draft sometimes some content also. I tired following things:-

=> I disabled all plugins and tried but it is not working

Strangely it is working with Live writer, i am able to save and publish new post using Live writer, but the same is not possible when i am using wordpress panel. I upgraded automatically. I used 3rd party hosting.

Thanks
Pranay