i've been running into some strange errors involving a project using #include while running it on windows instead of my usual linux environment. i've isolated the problem to line ending convention: an external file that uses the windows CrLf convention, but is otherwise the same as a file that works with no problems, will cause errors. here is the text of the external file i used:

local function _draw()
    cls(1)
end

to see the problem, save this with an external text editor using windows line ending convention (wordpad works, as do many programmer text editors) and use #include to include it in a cart.

Does your file have a .lua extension? You may try .p8 instead (see this previous bug report for details: https://www.lexaloffle.com/bbs/?pid=63569)