Michael,
I posted all the code for both the PLC and AdvancedHMI application.
It is a little complicated if you are new to PLC and .Net programming. The security validation is in the PLC logic. The operator enters a numeric value through AdvancedHMI. In the PLC confirms the entered password it turns on a bit. The data entry control I modified only allows data entry if the PLC bit is true.
It might be a little too complicated, but I posted all the code if you want to copy it.
Good Luck,
Steve