Thank you Graham, really appreciate your advice. I think I do need to learn more about Content Controls. I chose Active-X controls because my organisation has a range of older and newer versions of Office & I guess I'm just a novice at VBA and found Active-x easier to programme (previous experience with Excel VBA).

Perhaps interestingly my document had been working fine for several months. I ended up trying the same document on my home PC last night (Office 2013) and it works just fine - so it almost seems like it's something with my laptop?

I also tried your code but after the full code ran once, the Checkbox was still behaving oddly. The document definitely isn't in design mode, but I still have to manually toggle Design mode to be able to un-check the box and run the code. Other Checkbox's, don't think seem to have the problem. The other seemingly odd thing is that if I test multiple times, then it seems to 'behave'.

If I was to convert to Content Controls, one of the current actions for some checkboxes is to check the value of other checkboxes and it they're not checked, then the code will check them then run the code assigned to that next Checkbox. I can do this easily with Active-X but I couldn't get it to work with CC's. Would you be able to offer some advice on this to get me in the right direction?

Regards Corin.