It is not possible to access some menu's, such as the 'Preference' menu when there is a disc in the machine. In other cases, this may occur when the current settings on the machine prohibit access to certain areas.
For example, if 'Component' output is selected, the option relating to the scart output will not be accessible. This is because the machine will only output the picture by one of these two connections. The picture will always be outputted by the composite output, irrespective of the settings on the machine.