When moving to a different hosting provider, or doing some housekeeping with shared databases, sometimes it’s necessary to change the wordpress table prefix (the ‘wp_’ bit, by default) to something else. The table rename is easy enough, but after the rename, when trying to use your admin panel you will likely be greeted with a message saying:
Sorry, you are not allowed to access this page.
This is a small undocumented knock-on from the table name change, as there is also an option value that you need to change too. The _options table has an option called ‘wp_user_roles’, which also needs to have its prefix changed to match the tables. Do that and all should come good.
In case you’re interestered this option defines the user roles available to your users. Without it users can’t have assigned roles, and hence they have no permissions for any administrative function.