Beginner trying to construct a menu script.
eg
method open (var eventInfo Event)
var
mainMenu Menu
utilPU PopUpMenu
endvar
mainMenu.show()
endMethod

Consistently get error msg "Cannot change a built in header"

Won't work on any action (run, open, etc)

Can you suggest a sample menu script that will work?

If you don't add any command to the menu object, then surely it would not function...

Where are you putting this code? You should put it in a form's open method...