Assuming that you are using FileMaker 12 or newer, there's a script trigger, OnTabSwitch that is tripped when a user selects a panel in a tab control or slides a slider to a new panel. There are get functions (they aren't named exactly the same in FileMaker 12 and 13) that can detect the object name and number of the tab panel selected when the trigger was tripped so you can set up a script that displays a custom message whenever a user clicks on a specific tab panel. This script can even use go to object to return the user to the previous tab panel so that they never see the <<No access>> fields on that tab panel.
This is also possible in older versions though the scripting becomes a lot more complex.
Great! Thank you. And yes, I am using FileMaker Pro 12.