Are you still on the same IP address. I was checking an old domain name to see if it was worth buying and when I checked the cache of it in yahoo it said IP Banned. Did a site search not all the cache pages showed ip banned but 1. I think I looked at 10 or so really can't remember but that was the first time I have ever encountered that.
There is definitely an IP address issue with Yahoo. I have had a load of domains "banned" from their index. There were about 14 domains all on the same IP, all with unique content (news, reviews, forums, etc.) One day I noticed that there was no traffic coming from Yahoo for all but one of the domains. Once they were moved to their own IP addresses they were back in the index.
Inktomi marked us as breaking guidelines because they considered some of our text "too small". Fine, we made it a little bigger. No change. Since then, that site has never ranked in Yahoo. How long ago was Inktomi? 5 years?
How do you get a site back in Yahoo after it was banned by a different company so long ago?
At this point in time you simply wait until Bing's SERP's are displayed on Yahoo.