Wan2 in 60d

I have some problem with my fortigate, I'm using Fortigate 60d. And now I have 2 ISP which is I using in wan 1 and wan 2. The problem is, I can't ping my ip public in wan 2 from the outside. But when I switch my wan 2 into wan 1, I can ping it. But still the wan 2 which is I move from wan 1 can't ping. Can you help me pls? Current Running Firmware: FGT60D-5.00-build292.