So in an older version, I've used this mode pretty well, was great fun. Now I wanted to use it in the 1.1 on an already established map. Every time I open the Controller the Map Crashes and I get thrown into the Main Menu.

Crash Report:
The mod Schall Railway Controller (1.1.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event SchallRailwayController::on_gui_click (ID 1)
SchallRailwayController/lib/RClib.lua:359: attempt to index local 'status_info' (a nil value)
stack traceback:
SchallRailwayController/lib/RClib.lua:359: in function 'get_train_status_code'
SchallRailwayController/lib/RCgui.lua:274: in function 'frame_main_refresh'
SchallRailwayController/lib/RCgui.lua:388: in function 'frame_main_create'
SchallRailwayController/control.lua:47: in function <SchallRailwayController/control.lua:28>

Thanks for reporting.
The cause was I have omitted the new train state "destination full", which is newly introduced in game 1.1.0.
Should be fixed by 1.1.3.