asp.net mvc 3 route problem

when I browse http://localho开发者_运维百科st:4716/users/, it will show error:

Server Error in '/' Application.
The resource cannot be found.

but when I browse http://localhost:4716/users/index, it will ok.

other controllers all ok with or without /index, only UsersController doesn't work. anyone have similar problem?

[I didn't modify the Global.asax.cs after it auto-generated when project created. all route is default.]

Thanks a lot.