Steps to reproduce :

- import the package attached in the edit
- go to Unity > Preferences and make sure Auto Refresh is checked
- open the Vuforia 4 scene
- click on ImageTargetTarmac
- in the Inspector right click on Default Trackable Event script and choose edit script
- go to line 74 and press enter 3 times
- save the script
- go back to the editor and Unity will crash

*Note:
Video attached in the user's last reply.
It does not crash if Auto Refresh is not checked.