In the CHDK/SCRIPTS directory the two files are named usb_interval.lua and usb_interval (1).lua.
In the camera display, the extensions and part of the names are cut off. At the top of the page both files are labeled `_usb_interval~ and the different times distinguish them. They are directly below bas files and, when run, just start and stop, doing nothing.
At the bottom of the page, the files are named usb_interval (~ and usb_interval.l,again distinguished by the times. They are below lua files. These both run, the usb_interval file giving the uBasic error.