For some reason, I keep having this error when attempting to add GMLive to a preexisting Game Maker Studio 1 engine, and I can't figure out what the issue is. I've followed the instructions on setting it up- made the blank object/room, put obj_gmlive in the first room of the project, added the appropriate code to the create  event... I legitimately have no idea how to fix this. Any help would be appreciated.

Hello, what errors?

The GMS1 version of the extension hasn’t been updated in a little bit (and probably cannot be updated - the IDE falls apart while trying to do most things with it), but I think room reloading generally worked at the time.

Thought I posted an image of this, apparently it didn't. Here it is.
The first room of the project (called rmInit) has the code "room_set_live(rmInit, true);" in its creation code. The only thing i can think of is that that room's only used for a Global Control object to set a bunch of variables before moving to a proper title screen, so maybe that's the issue?
(And of course, Obj_GMLive is present in that room...)

That suggests that you send the game to rm_blank without using room_goto_live.

The first room of the project (called rmInit) has the code “room_set_live(rmInit, true);” in its creation code.

I wouldn’t recommend live-reloading the room that creates obj_gmlive (and probably the rest of your persistent objects) unless you’re willing to deal with consequences of doing so.

Okay, so as it turns out I'm a dip and messed up by putting RmBlank above the first room by accident.
Turns out there's no problems with GMLive in this case. My bad, sorry!!