I am able login to my site as an Administrator. However, anyone I designate as an Author or Editor can NOT login. They only get a white page that says: “You do not have sufficient permissions to export the content of this blog.”
– deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the Twenty Ten theme to rule out any theme-specific problems?
– resetting the plugins folder by FTP or phpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.