I have a 7140 router that came with IOS 12.1. Under the advisement of several sources, we upgraded to version 12.3 and the upgrade was successful. Although, originally we had the router configured properly and running in a live environment using version 12.1. Since the upgrade to version 12.3 one of the fastE interfaces will not come up. I know the interface is physically OK because I used it to config the router. I know this is a very broad question and I would only expect a broad answer, but can anybody think of any reason an interface would come up using 12.1 and not in 12.3? I am using the 100% identical running-config. My guess is that something in ver. 12.1 was, or was not, implied, compared to version 12.3. Any help or direction would be greatly appreciated. I am at a standstill right now now. Thanks in advance.
--Matt