Hard to tell what is the issue without seeing more code. What control is the sizeMenu? Have you put in an alert or $.writeln() to see if dlgIni has a value? If so, does sizeMenu have an item with that index?
Thanks for taking the trouble. I too inexperienced to deal with the reply!! Maybe I wasn't clear in my question. When I have a photo ready in Photoshop CC, I try to run the action and I get a pop up message as originally described. I enclose another screen dump showing the Actions and part of the photo I was trying to label.
The thing is you or someone else added that action to your default action set and it uses some script we know nothing about. You need to find the name of the script and read its code.
I see this in the web Meta Stamp
Actions and scripts have dependencies they will fail it not meet.
Thanks everyone. I have deleted the action and reinstalled and all is well now.