Sometimes after Magento modules installation, you can see 404 page not found error in your Magento administration zone.
To fix this error, try to re-save permission role of your administrator user, using Magento admin zone -> System -> Permissions -> 'Roles' page -> Administrators -> Click on 'Save Role' button.
Don't forget to clear Magento cache after this.
http://pradhab.blogspot.com/2013/03/magento-404-error.html