Thaks for that tip Sachin.

While my earlier card was locked in pretty good, I did change my card (moved to 8GB) and so carefully pushed it all the way in till it locked in.

Now strangely the lock-ups seem to be less (not gone).

Sometime, just sometimes while doing something, it will still lock up and freeze and I have to unlock with the lock slider (N810).
But definitely much lesser occurances now.