I am trying your solution and keep getting 'UpdateTextBox' is undefined when I preview the form. Here is what I am currently doing:
1. Modified calculated control formula to this:
it should work this way....
hopefuly you haven't taken/copied "<Exististing formula>" literally and you've replaced it with your real formula...
have you copied function code to a global scope, ie. out of any function or event handler you might have already had in form settings.
have you checked developer consoile for any errors?
My existing formula is similar to this:
lookup("Field1","ID", parseLookup(ControlName,false), "Recipients")
I was getting an error saying "Recipients is undefined" with this code. So I used the "Insert Reference" to put the Recipients field in the code. And now it's back to the "UpdateTextBox is undefined" error.
I got this copied over to a dev environment so I can save my work and not disrupt the live form that people are using.