Access to a File via HTTP and UNC failing using Web Application

[xontherocks]

I am working with a system that has 2 parts, one is an interface running like a Windows Service, and other is the Web App.

Both try to access to a server that is in the same network but has different domain, when the interface try to access via UNC to a network shared on the remote server it's work fine, but when the web application try to access to the same network folder using UNC don't do anything, does not throw an error, nothing, i tried to access the folder using HTTP but it is not work neither.

I read about to create a user in the remote machine with the same username and password of my IIS server, but when i tried to change the password to my IUS_XXX, i screwed everything here. I am pretty sure is a permission issue, but can you tell me some tips about the places that i need to review?

Thanks
XOTR