Akeeba Backup for WordPress has strict access control which only allows the most trusted levels of site users to access its interface: Administrators on single site installations and Super Admins in multisite installations. First check that you are accessing Akeeba Backup as a user of this Role.
Furthermore, these checks are performed by checking the user's
Capabilities, not their Role. If you get an error about not having adequate permissions to access this page it's Akeeba Backup telling you that your user does not seem to have the necessary Capabilities. I've seen that twice before, once four years ago and once more yesterday. In both cases it was a problem is with mapping capabilities to user roles in WordPress. This can be manually fixed using a plugin such as
Members to fix Capabilities to Role mapping.
Please note that Capabilities to Role mapping is
never, ever touched by Akeeba Backup itself. We do NOT change anything like that on your site. However, other plugins and even some themes do. It's very likely that one of the plugins or themes you installed did something stupid during installation, e.g. overwrite the "Administrator" Role's capabilities instead of adding to them, or directly manipulate the wp_user_roles entry in the wp_options table (containing a serialized data representation of the Role to Capabilities mapping) instead of going through the WordPress API. Finally, if you used a theme's prebuilt "quickstart" site to start developing your site it's possible that the problem simply existed on the prebuilt site.
If you did not get an error message stating you do not have adequate permissions please
enable WordPress' debug mode and access the page again. It should now print much more information. Either copy and paste it here or save the page as a PDF and attach it to your next reply. It will tell us exactly what was going on when the error page appeared. For example, you may be having an issue with cookies on your browser which causes the session identifier to be reset on every page load, rendering most features of Akeeba Backup inoperable (for very good security reasons; it's the same reason WordPress uses nonces to prevent cross site scripting a.k.a. XSS attacks).
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!