When you open the "Train Schedule" and then pause the game, it will crash after clicking "View locomotive" with the error "Cannot add child widget because it is NULL".
Here is a scenario and a savegame of it if required:
[0.10.3][slpwnd] Crash: View locomotive when game paused
Re: [0.10.3][slpwnd] Crash: View locomotive when game paused
Thanks for the report. This is related to issue https://forums.factorio.com/forum/vie ... =48&t=2277. Both issues will be solved in 0.10.4 by having proper "pausing" of the gui. No tooltips, not possible to click buttons, etc. In short the front gui will have modal focus when the game is paused or in menu.