They can happen! Trust me! I'm waiting to have my gallbladder out! The doctor has put it down to losing a large amount of weight in a short amount of time and I know of about four other people that have had the same thing whilst doing a VLCD...BUT don't let it scare you, they can happen any time to any one for any amount of reasons, for two weeks of on off pain, a hospital stint and a routine operation I would do it all over again even if someone told me I was going to go through it.
I had a very high fat diet before doing a VLCD and got told that I was likely to get them anyway because of that. My story does sound a little like a horror story but please please don't let it put you off, you know your body and if you don't feel well doing it see a doctor.