Hi
I had the same problem when building a new server and transferred my WP sites across. I found in my logs that it was a apache error with PHP.
mod_fcgid: HTTP request length 131100 (so far) exceeds MaxRequestLen.
To Fix I added MaxRequestLen 15728640 which is 15MB to the following file
/etc/apache2/mods-available/fcgid.conf and restarted apache.
Hope this helps
