Duplicate emails appear in my Windows Live inbox

I have been using Windows Live Mail together with my SBC Global DSL account. SBC Global (now AT&T) uses Yahoo as the email provider for their account holders. Originally I set up Live Mail to receive emails from my SBC account as well as my Gmail account. Also, I have another address which is forwarded to my SBC account.  I did not have a problem with this setup for the better part of five years but last week due to some changes that Yahoo instituted some of my emails were getting lost in the forwarding process. This is not acceptable as this is work related. As I do not like the thought of changing my ISP I changed the "forward to" address on the business related account from "address @ sbcglobal.net" to "*** Email address is removed for privacy ***". Everything works well except now I'm getting two emails in my inbox and I can't figure out a way to get rid of the duplicate. Thanx for your help