I played your save. It appears you have already collected the key and used it on the machine room door (the door is unlocked) - I'm guessing the glass jar re-spawns and the painting resets when you re-enter the guest room (but the key doesn't), which may be causing some confusion. You can just head on over to the machine room and it should already be open.
Try the following fix if the machine room door is locked for you:
Spoiler below!
open up your save file (the one you uploaded) in a text editor with line numbers (like notepad++) and go to line 18003 (or search "level_wood_4" and scroll up a little bit). You should see the following line: