Hi Kevin,

You can achieve this using form rules.

Click on the field you want the rule to affect (in my case I've made two yes/no fields, one called Tickbox1 and the other Tickbox2). I want Tickbox1 being ticked to make Tickbox 2 inactive, so I'm clicking on Tickbox2. Make sure when you click these fields, you've given them a name in the properties panel on the right. We'll use these names to reference the fields in our rule.

Once a field is clicked, this should change the ribbon at the top of the page from the 'designer' tab to the 'control' tab. Here you'll see an option called Add rule - click on it. This opens up the rule pane on the right.

The rule name can be whatever you like, it's best to name it a short summary of what the action does such as 'Disable Tickbox2' for easy finding later on.

In the 'when' field, click the f(x) button to open the full formula editor. There are many options in here, but what we're going to want for this case is relatively straightforward. First go to the 'named controls' tab and double click Tickbox1 to add it to the formula (will only be here if you gave the field a name as stated above). then type ==. You can also go up to the operators tab and add it by double-clicking on it there, this sign just represents 'equality' in programming. Finally we'll want to type the word true or the number 1. This is because Yes/No is represented internally by a boolean value (true/false, 1/0).

In full our rule should now look like:    Tickbox1==true

Clicking 'OK' to apply and exit the formula builder, go to the then field just below when and click 'Disable'. Our rule now reads something like "When Tickbox1 equals true/1/yes, then disable Tickbox2".

Hope this helps,

Sam