[RMMV] NEED HELP WITH MOVING BACKGROUNDS

So I've used this plugin for moving battle backgrounds before, but for some reason I can't get it to run anymore.
This is the plugin

So it is very simple to use.
All you need to do is select whatever background you want, put what speed you want it to scroll at the Troop's name which I've clearly done here :


But it just doesn't seem to work for some reason.
This here is the error I get.


Anyone think they could help me out here or perhaps know any other alternatives?
Thanks in advance!