A crash occurs when one attempts to enter TheLab from The Blueprint Designer Lab mod while the Signal Controlled Trains mod is active. Unloading Signal Controlled Trains allows access to TheLab issue free. Since the issue is a cross-mod one I have made this report on the pages for both mods.

Here is the error log:

The mod The Blueprint Designer Lab (1.0.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event BlueprintLab_design::on_gui_click (ID 1)
The mod Signal Controlled Trains (1.1.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Signal_Controlled_Trains::on_surface_created (ID 63)
Signal_Controlled_Trains/scripts/surfaces.lua:10: attempt to index local 'surface' (a nil value)
stack traceback:
Signal_Controlled_Trains/scripts/surfaces.lua:10: in function 'add_surface'
Signal_Controlled_Trains/scripts/main.lua:149: in function <Signal_Controlled_Trains/scripts/main.lua:148>
stack traceback:
[C]: in function 'create_surface'
BlueprintLab_design/scripts/init-lab.lua:6: in function 'InitLab'
BlueprintLab_design/scripts/logic.lua:11: in function 'OnLabButton'
BlueprintLab_design/scripts/gui.lua:46: in function <BlueprintLab_design/scripts/gui.lua:44>

Thanks for the report! I'll look into it asap :)

judging from the report, it looks to be on my end.

Should be fixed in the latest release

Thanks for the speedy fix!