I'm using the WordPress 2.2.3. I decided to upgrade to 2.3.1 today. But when I uploaded all files and upgrade the database, the version still 2.2.3. I tried to clear cache but the version is 2.2.3.
After that, I looked in the the source code, here are two results in wordpress\wp-includes\version.php
+ wordpress-2.3.1.zip: $wp_version = '2.2.3';
+ wordpress-2.3.1.tar.gz: $wp_version = '2.2.1';
It seems you forgot to change the version in the php file ?