WordPress has this particular problem when publishing or saving a blog post where it shows a 404 page instead of the required effect. This is irritating when you have typed a long post and just after you have published it shows the 404 error, and all your data is lost. I have faced this same problem for many times.
After a bit of Googling, I found out that the problem is with mod_security being set on server.
To fix this, add the following two lines in our .htaccess file.
SecFilterEngine Off<br />
SecFilterScanPOST Off
This should fix the problem. Let me try publishing this post.