Maybe the Sketch has an unidentifyable character in it. Probably in the first line. Might be some Text like license disclaimer or similar. Try creating a new Sketch without unneccessary Text and if that works, Look at Home at a copy of the Sketch that doesn‘t Open and See what character is at positions 8-10. Or maybe line 8-10… and try removing Charakters that aren‘t needed or Look like they are not supported on all Systems.
Also, what operating Systems are we Talking about? Always the Same, or is your Home System Windows and the School System Linux? Or how is it?
Also, try looking online at UTF-8 charset. Maybe you See some characters in your code that aren’t supported.