Mine did this when I first got it. In my case, what happened was when the dealer assembled the machine, they didn't get the metal "latches" (for lack of a better word) to slip over top of the catches on the sides of the gas tank on one side.
Once I figured this out, it took a bit of fiddling, but I got both of them to latch. Now that it's been on there a while like that, it's easy to get back in place whenever I remove the front plastic.
My best suggestion is to remove your front plastic (three screws to remove it -- one on each side of the front framrail below the screw that adjusts the headlight aiming, and one in the middle which is reached in the "forehead" of the machine, through the opening in that black area), and then unplug the headlights and the whole front end comes right off.
Once you see what I'm talking about, you should be able to see how to correct the problem.
Rob