Update: I might have figured out what caused my error earlier.
It occurs when
1.) I open a second "Download.bat" window before the first one has started to display a download progress bar. Essentially when I'm trying to start a second download before the first one even properly commenced.
and
2.) When I open too many downloads at the same time, I think my max was 8 and at the 9th Download.bat window the program just gave up on me and couldn't load the simulation engine any more.
Even though I don't know how to fix it, it's pretty easily avoidable, all in all.