Set Variable [$FilePath ; value: Get ( DesktopPath ) & Software::Store DMG 1 & ".DMG" ]
Export Field Contents [$FilePath ]
You won't need the & ".DMG" extension if this text is already part of the text in your field.
For more on $Path variables, container fields and what script steps can use a $Path variable, see this thread: Exploring the use of a $Path Variable in Scripts
Phil, Thank you for this reply. I still get that error dialogue box. Since the file is a ".dmg" file I suppose it is considered to have the text in the field.
I enclose this screen shot of the script to see what I am doing wrong.
IF software::Store DMG 1 is the name of your container field, you can't use it in the set variable step as the text referring to your inserted file in the container might be a lot more text than just the name of the file. Often, tables have a second field with the name of the file in it and that's what I had assumed was the case here.
But File names can be extracted from container fields. See this thread for a calculation that extracts the name of a file as well as a lot more info on $Path variables, container fields and script steps that can use them: