I don't see the harm in having more than one if u wish. You might not see the same results as you would if you were following the diet 100% to the letter but I would be very surprised if you didn't lose anything because you had a bar instead of a shake or something.
The strawberry shakes are actually higher in carbs than a bar (thats the only one I compared) so I've quite often had more than 1 bar a day as I find them more convenient! x
I've had 2 bars in one day before for the convenience of it cuz I was out and about all day....I think as long as you didn't do it everyday then in shouldn't affect your weight loss too much! xx