I am constructing a form giving parents the chance to sign up their children for various school clubs. What I would like to do is limit the amount of people ticking in the DECISION BOX to, say 20.

 

I have tried a script for this, but I cannot get it to work, as it continually throws back errors at me.

 

This is the script I use:

 

if(count(input.Drop_in_Computers_Y3_8_Monday_lunch_1250_1315_ICT_Suite_01)>= 20)        {        alert("This club is full. Please untick and resubmit your form.");        cancel submit;        }        }

Help!