User cannot access any tabs and/or fields.
Navigate to the staff record, and Edit. Use the lookup icon to locate and select the active User. Once the Active User is selected, Save the staff record.
If this does not resolve the issue follow these steps:
Navigate to Setup > Manage Users > Users, then select the user with the error. Scroll to Permission Sets Assignments, and add the Minimum Access permission set.
One of two issues can cause this error:
1) The user record and the staff record are not linked.
2) There are no permission sets assigned to the user record.