How much is too much exercise?

I'm trying to lose a bit of weight nothing too extreme just a little around my stomach, thighs and to tone up a bit. I've changed my diet and I'm currently doing a 50minute workout daily but my friends have been telling me that 50 minutes a day is too much and can be bad for you to exercise so much, is 50 minutes a day too much?
How much is too much exercise?
Post Opinion