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.
Seems that something wrong with SEO URLs engine in your Magento, try to disable this feature.
If the issue is still there feel free to contact our support.
i have been ignoring this minor problem for a month now and finally decided to look at it today and not 5 minutes later you have solved the problem.
Not a big deal but quite the annoyance!
thank you,
-Phil