Shown in the log:

[WRN 21:06:39.990] [HighLogic]: =========================== Scene Change : From EDITOR to SPACECENTER =====================
[EXC 21:06:39.995] NullReferenceException: Object reference not set to an instance of an object
MuMech.MechJebCore.Update ()

Game version: 1.1.2 (32 and 64 bit)
Mod Installed: MechJeb2 DEV #590, Exception Detector

Procedure:
1 - Go to VAB
2 - Place any part.
3 - Attach the "AR202" module to the part placed in step 3.
4 - Exit the editor.

The NRE will happen. Note that if you clear the editor via the "New" button and then exit, the error do not happens.