Default permissions on /etc/fuppes are root:root rwxr-xr-x,s o the fuppes daemon (running as user fuppes) cannot create the uuid.txt file.
This is because although the instructions on the wiki for setting up the user 'fuppes' say
sudo chown fuppes:fuppes /etc/fuppes/*
sudo chown -R fuppes:fuppes /var/lib/fuppes
the uuid.txt file doesn't exist at that point.