Yes or No selected on form drives next control

[smg]

I have a yes/no checkbox in a subform. If a user checks the checkbox, I want to disable the next control so they are unable to select from it's multi-select combo box, called Error Precursors. If the user does not check the checkbox I want them to have to select from it's multi-select combo box. Is this something I can do with validation rules?
Attached is my db, please see the frmBehaviorsSubform.

[pbaldy]

The disabling I'd do with this type of thing:

http://www.baldyweb.com/ConditionalVisibility.htm

I don't think the validation can be done with a rule. I'd have code in the before update event:

http://www.baldyweb.com/BeforeUpdate.htm

[smg]

I am having trouble making this work, would you be able to show me how to accomplish this in the database I attached to my initial post on this subject?

[pbaldy]

Why don't you post an updated database with your efforts and we'll fix it?