Script fails saving file with 'could not save a copy'

I wrote my friend a script to save an animation timeline frame as a JPG. It runs fine on my Windows VM, but on his mac he gets an error  dialog "SyntaxError: General Photoshop error occurred. This functionality may not be available in this version of Photoshop. - Could not save a copy as 'frame_1.jpg' because write access was not granted." He said other adjacent scripts I wrote can write out PSDs and such, but not this sciript (Frames to JPGs.txt, renamed from jsx to txt for upload).  

He's on a mac with 24.4.0 and Photoshop 2023. 

Any clues why he's getting this error while other scripts work?