“unknown function…” (but it IS known!)

I am using Duplicator (Lite) to try and migrate my site from local to my hosting service. After a successful install of the archive file, I get a fatal error when I try and load the homepage “Uncaught Error: Call to undefined function simone_social_menu() …”
(for full error message, see above link)

Examining my code for where this function is defined, it IS defined..buried in another subdirectory, but apparently PHP does not know it is there. (I tried to print out debugging statements to show the path, but did not help…)

This does not happen in my local environment, so…what could be the connection between using Duplicator and installing this at my hosting service to cause this error?

thanks for any help,
rcx

The page I need help with: [log in to see the link]