The error logs can be extremely helpful. In my case, I had the following error:
“PHP Fatal error: Allowed memory size of 33554432 bytes exhausted”
I fixed it by increasing my memory limit (just for wp-admin) in an .htaccess file in [root]/wp-admin like this:
php_value memory_limit 64M
Oddly, it works fine on my install, but a client of mine installed the same version of WordPress and gets this error (same server, same Apache install, same setup for both sites in the Apache vhosts.conf file.
[UPDATE]
My Apache is being strange, but I just added this to the client’s vhosts.conf config and it’s all better:
<Directory /home/sites/<domain>/www/htdocs>
AllowOverride AuthConfig Options FileInfo
</Directory>
