When you are analysing a position where there is a check, making a null move will create an invaled fen and the engine will close abruptly. Moreover, you won't be able to save the game.
Posted with 1 priority as you can just CONTROL+Z to undo it.
I'm using SCID 4.5.2 (the one in the wheezy repositories in Debian).
Rigao.
Thanks,
fixed with commit:
http://sourceforge.net/p/scid/code/ci/c6486ea2f0f12d82b3535de2b1cbbd16eb6d65ef/