WP Dashboard Won't Load After Transferring Site

I just migrated a site from my development server to a client's hosting environment. The site loads fine however when ever I try to go to the WP dashboard the browser will search for around 3 minutes and give up showing a 404.

I migrated based on the recommended instructions from wordpress.org.

- exported DB and imported on new site
- copied all files over with FTP
- changed wp-config database params
- used phpMyadmin to change site url and home url manually
- used the URL rewrite tool from interconnect/it to rewrite all URLS

Just wondering if there is something simple that I'm missing that could have caused this.