url problem

[Goomzee]

anybody please tell me why my below forum url is not working
http://www.mknexusonline.com/forums

and below forums works fine

http://www.mknexusonline.com/forums/index.php

whereas i set Forum URL is http://www.mknexusonline.com/forums from vbulletin options and when i click http://www.mknexusonline.com/forums it's automatically redirect me here
http://www.mknexusonline.com/forums and page not showing.