Lock field based on another field
On my Payment layout, I have a field named "payment type". This field is a pop-up menu with two choices. The choices are "Client" and "Group". I also have two fields named "Client list" and "Insurance List".
When I choose "Client" from the pop-up menu I would like to have the "Insurance List" field locked (disable the user from entering). And visa versa, when I choose "Group" from the pop-up menu I would like to have the "Client List" field locked.
Seems simple enough?
Any help would be greatly appreciated