Very likely a key binding intercepted by the desktop environment. What happens if you run the what-is command at the SlickEdit command prompt, and then hit Alt-F7? If nothing happens, SlickEdit is not even seeing the keypress.
I reinstalled over my debian/MATE VM last week, so I can't check to see what that keypress maps to though. On Ubuntu 17.10, Alt-F7 appears to be a shortcut for "move window", so I can't use it as an application shortcut here either.
