A permissions error inside WordPress.
WHAT IT MEANS
Your user account does not have the capability required for that page.
THE COMMON CAUSES
Your role was changed, or is not Administrator A plugin modifying capabilities A corrupted user role definition in the database A plugin conflict after an update
CHECKING YOUR ROLE
If you can reach the users list, check your own role.
If you cannot reach anything, the role may have been changed or corrupted.
IF YOU LOST ADMINISTRATOR ACCESS
WP-CLI can promote a user to administrator in one command, if you have SSH access.
Otherwise, create a new administrator directly in the database, or add temporary code to functions.php that creates one, removing it immediately afterwards.
AFTER A PLUGIN UPDATE
A plugin managing roles may have reset them. Disable it by renaming its directory and check whether access returns.
AFTER A MIGRATION
Table prefix mismatch. WordPress stores capabilities with the prefix in the key name, so a prefix change makes your role invisible.
Correct the prefix in wp-config.php to match the actual tables.
