Hallo,
if I understand it right, you can access the web service from all over the Worlld with your public ip address, right?
And if you try to reach the web service from your local network with public ip address than it doesn’t work?
If this is the case, you need perhaps a Haripin NAT http://forum.mikrotik.com/t/hairpin-nat-routing/127862/1 or http://forum.mikrotik.com/t/hairpin-nat-the-easy-way/146718/1